CFRG S. Smyshlyaev, Ed.
Internet-Draft CryptoPro
Intended status: Informational R. Housley
Expires: September 8, 2017 Vigil Security, LLC
M. Bellare
University of California, San Diego
E. Alekseev
E. Smyshlyaeva
CryptoPro
March 7, 2017
Re-keying Mechanisms for Symmetric Keys
draft-irtf-cfrg-re-keying-01
Abstract
This specification contains a description of a variety of methods to
increase the lifetime of symmetric keys. It provides external and
internal re-keying mechanisms that can be used with such modes of
operations as CTR, GCM, CBC, CFB, OFB and OMAC.
Status of This Memo
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document authors. All rights reserved.
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Basic Terms and Definitions . . . . . . . . . . . . . . . . . 3
4. External Re-keying Mechanisms . . . . . . . . . . . . . . . . 5
4.1. Parallel Constructions . . . . . . . . . . . . . . . . . 5
4.1.1. Parallel Construction Based on a KDF on a Block
Cipher . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.2. Parallel Construction Based on HKDF . . . . . . . . . 6
4.2. Serial Constructions . . . . . . . . . . . . . . . . . . 7
4.2.1. Serial Construction Based on a KDF on a Block Cipher 7
4.2.2. Serial Construction Based on HKDF . . . . . . . . . . 8
5. Internal Re-keying Mechanisms . . . . . . . . . . . . . . . . 8
5.1. Constructions that Do Not Require Master Key . . . . . . 8
5.1.1. ACPKM Re-keying Mechanisms . . . . . . . . . . . . . 8
5.1.2. CTR-ACPKM Encryption Mode . . . . . . . . . . . . . . 10
5.1.3. GCM-ACPKM Encryption Mode . . . . . . . . . . . . . . 12
5.2. Constructions that Require Master Key . . . . . . . . . . 14
5.2.1. ACPKM-Master Key Generation from the Master Key . . . 15
5.2.2. CTR Mode Key Meshing . . . . . . . . . . . . . . . . 16
5.2.3. GCM Mode Key Meshing . . . . . . . . . . . . . . . . 19
5.2.4. CBC Mode Key Meshing . . . . . . . . . . . . . . . . 22
5.2.5. CFB Mode Key Meshing . . . . . . . . . . . . . . . . 24
5.2.6. OFB Mode Key Meshing . . . . . . . . . . . . . . . . 26
5.2.7. OMAC Mode Key Meshing . . . . . . . . . . . . . . . . 27
6. Joint Usage of External and Internal Re-keying . . . . . . . 29
7. Scope of Usage of Rekeying-Based Schemas . . . . . . . . . . 29
7.1. Key Transformation Rules . . . . . . . . . . . . . . . . 29
7.2. Principles of Choice of Constructions and Security
Parameters . . . . . . . . . . . . . . . . . . . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . . 32
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.1. Normative References . . . . . . . . . . . . . . . . . . 33
9.2. Informative References . . . . . . . . . . . . . . . . . 33
Appendix A. Test examples . . . . . . . . . . . . . . . . . . . 34
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
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1. Introduction
Common cryptographic attacks base their success on the ability to get
many encryptions under a single key. If encryption is performed
under a single key, there is a certain maximum threshold number of
messages that can be safely encrypted. These restrictions can come
either from combinatorial properties of the used cipher modes of
operation (for example, birthday attack [BDJR]) or from particular
cryptographic attacks on the used block cipher (for example, linear
cryptanalysis [Matsui]). Moreover, most strict restrictions here
follow from the need to resist side-channel attacks. The adversary's
opportunity to obtain an essential amount of data processed with a
single key leads not only to theoretic but also to practical
vulnerabilities (see [BL]). Therefore, when the total size of a
plaintext processed with a single key reaches the threshold, this key
must be replaced.
The most simple and obvious way for overcoming the key lifetimes
limitations is a renegotiation of a regular session key. However,
this reduces the total performance since it usually entails the
frequent use of a public key cryptography.
Another way is to use a transformation of a previously negotiated
key. This specification presents the description of such mechanisms
and the description of the cases when these mechanisms should be
applied.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Basic Terms and Definitions
This document uses the following terms and definitions for the sets
and operations on the elements of these sets:
(xor) exclusive-or of two binary vectors of the same length.
V* the set of all strings of a finite length (hereinafter
referred to as strings), including the empty string;
V_s the set of all binary strings of length s, where s is a non-
negative integer; substrings and string components are
enumerated from right to left starting from one;
|X| the bit length of the bit string X;
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A|B concatenation of strings A and B both belonging to V*, i.e.,
a string in V_{|A|+|B|}, where the left substring in V_|A| is
equal to A, and the right substring in V_|B| is equal to B;
Z_{2^n} ring of residues modulo 2^n;
Int_s: V_s -> Z_{2^s} the transformation that maps a string a =
(a_s, ... , a_1), a in V_s, into the integer Int_s(a) =
2^s*a_s + ... + 2*a_2 + a_1;
Vec_s: Z_{2^s} -> V_s the transformation inverse to the mapping
Int_s;
MSB_i: V_s -> V_i the transformation that maps the string a = (a_s,
... , a_1) in V_s, into the string MSB_i(a) = (a_s, ... ,
a_{s-i+1}) in V_i;
LSB_i: V_s -> V_i the transformation that maps the string a = (a_s,
... , a_1) in V_s, into the string LSB_i(a) = (a_i, ... ,
a_1) in V_i;
Inc_c: V_s -> V_s the transformation that maps the string a = (a_s,
... , a_1) in V_s, into the string Inc_c(a) = MSB_{|a|-
c}(a) | Vec_c(Int_c(LSB_c(a)) + 1(mod 2^c)) in V_s;
a^s denotes the string in V_s that consists of s 'a' bits;
E_{K}: V_n -> V_n the block cipher permutation under the key K in
V_k;
ceil(x) the least integer that is not less than x;
k the key K size (in bits);
n the block size of the block cipher (in bits);
b the total number of data blocks in the plaintext (b = ceil(m/
n));
N the section size (the number of bits in a data section);
l the number of data sections in the plaintext;
m the message M size (in bits);
phi_i: V_s -> V_s the transformation that maps a string a = (a_s,
... , a_1) into the string phi_i(a) = a' = (a'_s, ... ,
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a'_1), 1 <= i <= s, such that a'_i = 1 and a'_j = a_j for all
j in {1, ... , s}\{i}.
A plaintext message P and a ciphertext C are divided into b = ceil(m/
n) segments denoted as P = P_1 | P_2 | ... | P_b and C = C_1 | C_2 |
... | C_b, where P_i and C_i are in V_n, for i = 1, 2, ... , b-1, and
P_b, C_b are in V_r, where r <= n if not otherwise stated.
4. External Re-keying Mechanisms
This section presents an approach to increase the lifetime of
negotiated keys after processing a limited number of integral
messages. It provides an external parallel and serial re-keying
mechanisms (see [AbBell]). These mechanisms use an initial
(negotiated) key as a master key, which is never used directly for
the data processing but is used for key generation. Such mechanisms
operate outside of the base modes of operations and do not change
them at all, therefore they are called "external re-keying" in this
document.
4.1. Parallel Constructions
The main idea behind external re-keying with parallel construction is
presented in Fig.1:
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Maximum message size = m_max.
_____________________________________________________________
m_max
<---------------->
M^{1,1} |=== |
M^{1,2} |=============== |
+--K^1--> . . .
| M^{1,q_1} |======== |
|
|
| M^{2,1} |================|
| M^{2,2} |===== |
K-----|--K^2--> . . .
| M^{2,q_2} |========== |
|
...
| M^{t,1} |============ |
| M^{t,2} |============= |
+--K^t--> . . .
M^{t,q_t} |========== |
_____________________________________________________________
Figure 1: External parallel re-keying mechanisms
The key K^i, i = 1, ... , t-1, is updated after processing a certain
amount of data (see Section 7.1).
4.1.1. Parallel Construction Based on a KDF on a Block Cipher
ExtParallelC re-keying mechanism is based on a block cipher and is
used to generate t keys for t sections as follows:
K^1 | K^2 | ... | K^t = ExtParallelC(K, t*k) =
MSB_{t*k}(E_{K}(0) | E_{K}(1) | ... | E_{K}(J-1)),
where J = ceil(k/n).
4.1.2. Parallel Construction Based on HKDF
ExtParallelH re-keying mechanism is based on HMAC key derivation
function HKDF-Expand, described in [RFC5869], and is used to generate
t keys for t sections as follows:
K^1 | K^2 | ... | K^t = ExtParallelH(K, t*k) = HKDF-Expand(K,
label, t*k),
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where label is a string (can be a zero-length string) that is defined
by a specific protocol.
4.2. Serial Constructions
The main idea behind external re-keying with serial construction is
presented in Fig.2:
Maximum message size = m_max.
_____________________________________________________________
m_max
<---------------->
M^{1,1} |=== |
M^{1,2} |=============== |
K*_1 = K ----K^1--> . . .
| M^{1,q_1} |======== |
|
|
| M^{2,1} |================|
v M^{2,2} |===== |
K*_2 --------K^2--> . . .
| M^{2,q_2} |========== |
|
...
| M^{t,1} |============ |
v M^{t,2} |============= |
K*_t --------K^t--> . . .
M^{t,q_t} |========== |
_____________________________________________________________
Figure 2: External serial re-keying mechanisms
The key K^i, i = 1, ... , t-1, is updated after processing a certain
amount of data (see Section 7.1).
4.2.1. Serial Construction Based on a KDF on a Block Cipher
The key K^i is calculated using ExtSerialC transformation as follows:
K^i = ExtSerialC(K, i) = MSB_k(E_{K*_i}(0) | E_{K*_i}(1) | ... |
E_{K*_i}(J-1)),
where J = ceil(k/n), i = 1, ... , t, K*_i is calculated as follows:
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K*_1 = K,
K*_{j+1} = MSB_k(E_{K*_j}(J) | E_{K*_j}(J+1) | ... | E_{K*_j}(2J-
1)),
where j = 1, ... , t-1.
4.2.2. Serial Construction Based on HKDF
The key K^i is calculated using ExtSerialH transformation as follows:
K^i = ExtSerialH(K, i) = HKDF-Expand(K*_i, label1, k),
where i = 1, ... , t, HKDF-Expand is an HMAC-based key derivation
function, described in [RFC5869], K*_i is calculated as follows:
K*_1 = K,
K*_{j+1} = HKDF-Expand(K*_j, label2, k), where j = 1, ... , t-1,
where label1 and label2 are different strings (can be a zero-length
strings) that are defined by a specific protocol (see, for example,
TLS 1.3 updating traffic keys algorithm [TLSDraft]).
5. Internal Re-keying Mechanisms
This section presents an approach to increase the lifetime of
negotiated key by re-keying during each separate message processing.
It provides an internal re-keying mechanisms called ACPKM and ACPKM-
Master that do not use and use a master key respectively. Such
mechanisms are integrated into the base modes of operations and can
be considered as the base mode extensions, therefore they are called
"internal re-keying" in this document.
5.1. Constructions that Do Not Require Master Key
This section describes the block cipher modes that uses the ACPKM re-
keying mechanism, which does not use master key: an initial key is
used directly for the encryption of the data.
5.1.1. ACPKM Re-keying Mechanisms
This section defines periodical key transformation with no master key
which is called ACPKM re-keying mechanism. This mechanism can be
applied to one of the basic encryption modes (CTR and GCM block
cipher modes) for getting an extension of this encryption mode that
uses periodical key transformation with no master key. This
extension can be considered as a new encryption mode.
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An additional parameter that defines the functioning of basic
encryption modes with the ACPKM re-keying mechanism is the section
size N. The value of N is measured in bits and is fixed within a
specific protocol based on the requirements of the system capacity
and key lifetime (some recommendations on choosing N will be provided
in Section 8). The section size N MUST be divisible by the block
size n.
The main idea behind internal re-keying with no master key is
presented in Fig.3:
Section size = const = N,
maximum message size = m_max.
____________________________________________________________________
ACPKM ACPKM ACPKM
K^1 = K ---> K^2 ---...-> K^{l_max-1} ----> K^{l_max}
| | | |
| | | |
v v v v
M^{1} |==========|==========| ... |==========|=======: |
M^{2} |==========|==========| ... |=== | : |
. . . . . . :
: : : : : : :
M^{q} |==========|==========| ... |==========|===== : |
section :
<----------> m_max
N bit
___________________________________________________________________
l_max = ceil(m_max/N).
Figure 3: Key meshing with no master key
During the processing of the input message M with the length m in
some encryption mode that uses ACPKM key transformation of the key K
the message is divided into l = ceil(m/N) sections (denoted as M =
M_1 | M_2 | ... | M_l, where M_i is in V_N for i = 1, 2, ... , l-1
and M_l is in V_r, r <= N). The first section of each message is
processed with the initial key K^1 = K. To process the (i+1)-th
section of each message the K^{i+1} key value is calculated using
ACPKM transformation as follows:
K^{i+1} = ACPKM(K^i) = MSB_k(E_{K^i}(W_1) | ... | E_{K^i}(W_J)),
where J = ceil(k/n), W_t = phi_c(D_t) for any t in {1, ... ,J} and
D_1, D_2, ... , D_J are in V_n and are calculated as follows:
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D_1 | D_2 | ... | D_J = MSB_{J*n}(D),
where D is the following constant in V_{1024}:
D = ( F3 | 74 | E9 | 23 | FE | AA | D6 | DD
| 98 | B4 | B6 | 3D | 57 | 8B | 35 | AC
| A9 | 0F | D7 | 31 | E4 | 1D | 64 | 5E
| 40 | 8C | 87 | 87 | 28 | CC | 76 | 90
| 37 | 76 | 49 | 9F | 7D | F3 | 3B | 06
| 92 | 21 | 7B | 06 | 37 | BA | 9F | B4
| F2 | 71 | 90 | 3F | 3C | F6 | FD | 1D
| 70 | BB | BB | 88 | E7 | F4 | 1B | 76
| 7E | 44 | F9 | 0E | 46 | 91 | 5B | 57
| 00 | BC | 13 | 45 | BE | 0D | BD | C7
| 61 | 38 | 19 | 3C | 41 | 30 | 86 | 82
| 1A | A0 | 45 | 79 | 23 | 4C | 4C | F3
| 64 | F2 | 6A | CC | EA | 48 | CB | B4
| 0C | B9 | A9 | 28 | C3 | B9 | 65 | CD
| 9A | CA | 60 | FB | 9C | A4 | 62 | C7
| 22 | C0 | 6C | E2 | 4A | C7 | FB | 5B).
N o t e : The constant D is such that phi_c(D_1), ... , phi_c(D_J)
are pairwise different for any allowed n, k, c values.
N o t e : The constant D is such that D =
sha512(streebog512(0^1024)) | sha512(streebog512(1^1024)), where
sha512 is a hash function with 512-bit output corresponding to the
algorithm SHA-512 [SHA-512], streebog512 is a hash function with
512-bit output, corresponding to the algorithm GOST R 34.11-2012
[GOST3411-2012], [RFC6986].
5.1.2. CTR-ACPKM Encryption Mode
This section defines a CTR-ACPKM encryption mode that uses internal
ACPKM re-keying mechanism for the periodical key transformation.
The CTR-ACPKM mode can be considered as the extended by the ACPKM re-
keying mechanism basic encryption mode CTR (see [MODES]).
The CTR-ACPKM encryption mode can be used with the following
parameters:
o 64 <= n <= 512;
o 128 <= k <= 512;
o the number of bits c in a specific part of the block to be
incremented is such that 32 <= c <= 3/4 n.
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The CTR-ACPKM mode encryption and decryption procedures are defined
as follows:
+----------------------------------------------------------------+
| CTR-ACPKM-Encrypt(N, K, ICN, P) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - key K, |
| - initial counter nonce ICN in V_{n-c}, |
| - plaintext P = P_1 | ... | P_b, |P| < n * 2^{c-1}. |
| Output: |
| - Ciphertext C. |
|----------------------------------------------------------------|
| 1. CTR_1 = ICN | 0^c |
| 2. For j = 2, 3, ... , b do |
| CTR_{j} = Inc_c(CTR_{j-1}) |
| 3. K^1 = K |
| 4. For i = 2, 3, ... , ceil(|P|/N) |
| K^i = ACPKM(K^{i-1}) |
| 5. For j = 1, 2, ... , b do |
| i = ceil(j*n / N), |
| G_j = E_{K^i}(CTR_j) |
| 6. C = P (xor) MSB_{|P|}(G_1 | ... | G_b) |
| 7. Return C |
+----------------------------------------------------------------+
+----------------------------------------------------------------+
| CTR-ACPKM-Decrypt(N, K, ICN, C) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - key K, |
| - initial counter nonce ICN in V_{n-c}, |
| - ciphertext C = C_1 | ... | C_b, |C| < n * 2^{c-1}. |
| Output: |
| - Plaintext P. |
|----------------------------------------------------------------|
| 1. P = CTR-ACPKM-Encrypt(N, K, ICN, C) |
| 2. Return P |
+----------------------------------------------------------------+
The initial counter nonce ICN value for each message that is
encrypted under the given key must be chosen in a unique manner.
The message size m MUST NOT exceed n * 2^{c-1} bits.
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5.1.3. GCM-ACPKM Encryption Mode
This section defines a GCM-ACPKM encryption mode that uses internal
ACPKM re-keying mechanism for the periodical key transformation.
The GCM-ACPKM mode can be considered as the extended by the ACPKM re-
keying mechanism basic encryption mode GCM (see [GCM]).
The GCM-ACPKM encryption mode can be used with the following
parameters:
o n in {128, 256};
o 128 <= k <= 512;
o the number of bits c in a specific part of the block to be
incremented is such that 32 <= c <= 3/4 n;
o authentication tag length t.
The GCM-ACPKM mode encryption and decryption procedures are defined
as follows:
+-------------------------------------------------------------------+
| GHASH(X, H) |
|-------------------------------------------------------------------|
| Input: |
| - Bit string X = X_1 | ... | X_m, X_i in V_n for i in 1, ... , m.|
| Output: |
| - Block GHASH(X, H) in V_n. |
|-------------------------------------------------------------------|
| 1. Y_0 = 0^n |
| 2. For i = 1, ... , m do |
| Y_i = (Y_{i-1} (xor) X_i) * H |
| 3. Return Y_m |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCTR(N, K, ICB, X) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - key K, |
| - initial counter block ICB, |
| - X = X_1 | ... | X_b, X_i in V_n for i = 1, ... , b-1 and |
| X_b in V_r, where r <= n. |
| Output: |
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| - Y in V_{|X|}. |
|-------------------------------------------------------------------|
| 1. If X in V_0 then return Y, where Y in V_0 |
| 2. GCTR_1 = ICB |
| 3. For i = 2, ... , b do |
| GCTR_i = Inc_c(GCTR_{i-1}) |
| 4. K^1 = K |
| 5. For j = 2, ... , ceil(l*n / N) |
| K^j = ACPKM(K^{j-1}) |
| 6. For i = 1, ... , b do |
| j = ceil(i*n / N), |
| G_i = E_{K_j}(GCTR_i) |
| 7. Y = X (xor) MSB_{|X|}(G_1 | ... | G_b) |
| 8. Return Y. |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCM-ACPKM-Encrypt(N, K, IV, P, A) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - key K, |
| - initial counter nonce ICN in V_{n-c}, |
| - plaintext P, |P| <= n*(2^{c-1} - 2), P = P_1 | ... | P_b, |
| - additional authenticated data A. |
| Output: |
| - Ciphertext C, |
| - authentication tag T. |
|-------------------------------------------------------------------|
| 1. H = E_{K}(0^n) |
| 2. If c = 32, then ICB_0 = ICN | 0^31 | 1 |
| if c!= 32, then s = n * ceil(|ICN| / n) - |ICN|, |
| ICB_0 = GHASH(ICN | 0^{s+n-64} | Vec_64(|ICN|), H) |
| 3. C = GCTR(N, K, Inc_32(ICB_0), P) |
| 4. u = n*ceil(|C| / n) - |C| |
| v = n*ceil(|A| / n) - |A| |
| 5. S = GHASH(A | 0^v | C | 0^u | 0^{n-128} | Vec_64(|A|) | |
| | Vec_64(|C|), H) |
| 6. T = MSB_t(E_{K}(ICB_0) (xor) S) |
| 7. Return C | T |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCM-ACPKM-Decrypt(N, K, IV, A, C, T) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - key K, |
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| - initial counter block ICB, |
| - additional authenticated data A. |
| - ciphertext C, |C| <= n*(2^{c-1} - 2), C = C_1 | ... | C_b, |
| - authentication tag T |
| Output: |
| - Plaintext P or FAIL. |
|-------------------------------------------------------------------|
| 1. H = E_{K}(0^n) |
| 2. If c = 32, then ICB_0 = ICN | 0^31 | 1 |
| if c!= 32, then s = n*ceil(|ICN|/n)-|ICN|, |
| ICB_0 = GHASH(ICN | 0^{s+n-64} | Vec_64(|ICN|), H) |
| 3. P = GCTR(N, K, Inc_32(ICB_0), C) |
| 4. u = n*ceil(|C| / n)-|C| |
| v = n*ceil(|A| / n)-|A| |
| 5. S = GHASH(A | 0^v | C | 0^u | 0^{n-128} | Vec_64(|A|) | |
| | Vec_64(|C|), H) |
| 6. T' = MSB_t(E_{K}(ICB_0) (xor) S) |
| 7. If T = T' then return P; else return FAIL |
+-------------------------------------------------------------------+
The * operation on (pairs of) the 2^n possible blocks corresponds to
the multiplication operation for the binary Galois (finite) field of
2^n elements defined by the polynomial f as follows (by analogy with
[GCM]):
n = 128: f = a^128 + a^7 + a^2 + a^1 + 1.
n = 256: f = a^256 + a^10 + a^5 + a^2 + 1.
The initial vector IV value for each message that is encrypted under
the given key must be chosen in a unique manner.
The message size m MUST NOT exceed n*(2^{c-1} - 2) bits.
The key for computing values E_{K}(ICB_0) and H is not updated and is
equal to the initial key K.
5.2. Constructions that Require Master Key
This section describes the block cipher modes that uses the ACPKM-
Master re-keying mechanism, which use the initial key K as a master
key K, so K is never used directly for the data processing but is
used for key derivation.
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5.2.1. ACPKM-Master Key Generation from the Master Key
This section defines periodical key transformation with master key K
which is called ACPKM-Master re-keying mechanism. This mechanism can
be applied to one of the basic encryption modes (CTR, GCM, CBC, CFB,
OFB, OMAC encryption modes) for getting an extension of this
encryption mode that uses periodical key transformation with master
key. This extension can be considered as a new encryption mode.
Additional parameters that defines the functioning of basic
encryption modes with the ACPKM-Master re-keying mechanism are the
section size N and change frequency T* of the key K. The values of N
and T* are measured in bits and are fixed within a specific protocol
based on the requirements of the system capacity and key lifetime
(some recommendations on choosing N and T* will be provided in
Section 8). The section size N MUST be divisible by the block size
n. The key frequency T* MUST be divisible by n.
The main idea behind internal re-keying with master key is presented
in Fig.4:
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Change frequency T*,
section size N,
maximum message size = m_max.
__________________________________________________________________________________
ACPKM ACPKM
K*_1 = K--------------> K*_2 ---------...---------> K*_l_max
___|___ ___|___ ___|___
| | | | | |
v ... v v ... v v ... v
K[1] K[t] K[t+1] K[2t] K[(l_max-1)t+1] K[l_max*t]
| | | | | |
| | | | | |
v v v v v v
M^{1}||========|...|========||========|...|========||...||========|...|== : ||
M^{2}||========|...|========||========|...|========||...||========|...|======: ||
... || | | || | | || || | | : ||
M^{q}||========|...|========||==== |...| ||...|| |...| : ||
section :
<--------> :
N bit m_max
__________________________________________________________________________________
|K[i]| = d,
t = T*/d,
l_max = ceil(m_max/N).
Figure 4: Key meshing with master key
During the processing of the input message M with the length m in
some encryption mode that uses ACPKM-Master key transformation with
the master key K and key frequency T* the message M is divided into l
= ceil(m/N) sections (denoted as M = M_1 | M_2 | ... | M_l, where M_i
is in V_N for i in {1, 2, ... , l-1} and M_l is in V_r, r <= N). The
j-th section of each message is processed with the key material K[j],
j in {1, ... ,l}, |K[j]| = d, that has been calculated with the
ACPKM-Master algorithm as follows:
K[1] | ... | K[l] = ACPKM-Master(T*, K, d*l) = CTR-ACPKM-Encrypt
(T*, K, 1^{n/2}, 0^{d*l}).
5.2.2. CTR Mode Key Meshing
This section defines a CTR-ACPKM-Master encryption mode that uses
internal ACPKM-Master re-keying mechanism for the periodical key
transformation.
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The CTR-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic encryption
mode CTR (see [MODES]).
The CTR-ACPKM-Master encryption mode can be used with the following
parameters:
o 64 <= n <= 512;
o 128 <= k <= 512;
o the number of bits c in a specific part of the block to be
incremented is such that 32 <= c <= 3/4 n.
The key material K[j] that is used for one section processing is
equal to K^j, |K^j| = k bits.
The CTR-ACPKM-Master mode encryption and decryption procedures are
defined as follows:
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+----------------------------------------------------------------+
| CTR-ACPKM-Master-Encrypt(N, K, T*, ICN, P) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initial counter nonce ICN in V_{n-c}, |
| - plaintext P = P_1 | ... | P_b, |P| <= 2^{n/2-1}*n*N / k. |
| Output: |
| - Ciphertext C. |
|----------------------------------------------------------------|
| 1. CTR_1 = ICN | 0^c |
| 2. For j = 2, 3, ... , b do |
| CTR_{j} = Inc_c(CTR_{j-1}) |
| 3. l = ceil(b*n / N) |
| 4. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 5. For j = 1, 2, ... , b do |
| i = ceil(j*n / N), |
| G_j = E_{K^i}(CTR_j) |
| 6. C = P (xor) MSB_{|P|}(G_1 | ... |G_b) |
| 7. Return C |
|----------------------------------------------------------------+
+----------------------------------------------------------------+
| CTR-ACPKM-Master-Decrypt(N, K, T*, ICN, C) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initial counter nonce ICN in V_{n-c}, |
| - ciphertext C = C_1 | ... | C_b, |C| <= 2^{n/2-1}*n*N / k. |
| Output: |
| - Plaintext P. |
|----------------------------------------------------------------|
| 1. P = CTR-ACPKM-Master-Encrypt(N, K, T*, ICN, C) |
| 1. Return P |
+----------------------------------------------------------------+
The initial counter nonce ICN value for each message that is
encrypted under the given key must be chosen in a unique manner. The
counter (CTR_{i+1}) value does not change during key transformation.
The message size m MUST NOT exceed (2^{n/2-1}*n*N / k) bits.
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5.2.3. GCM Mode Key Meshing
This section defines a GCM-ACPKM-Master encryption mode that uses
internal ACPKM-Master re-keying mechanism for the periodical key
transformation.
The GCM-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic encryption
mode GCM (see [GCM]).
The GCM-ACPKM-Master encryption mode can be used with the following
parameters:
o n in {128, 256};
o 128 <= k <= 512;
o the number of bits c in a specific part of the block to be
incremented is such that 32 <= c <= 3/4 n;
o authentication tag length t.
The key material K[j] that is used for one section processing is
equal to K^j, |K^j| = k bits, that is calculated as follows:
K^1 | ... | K^j | ... | K^l = ACPKM-Master(T*, K, k*l).
The GCM-ACPKM-Master mode encryption and decryption procedures are
defined as follows:
+-------------------------------------------------------------------+
| GHASH(X, H) |
|-------------------------------------------------------------------|
| Input: |
| - Bit string X = X_1 | ... | X_m, X_i in V_n for i in {1, ... ,m}|
| Output: |
| - Block GHASH(X, H) in V_n |
|-------------------------------------------------------------------|
| 1. Y_0 = 0^n |
| 2. For i = 1, ... , m do |
| Y_i = (Y_{i-1} (xor) X_i)*H |
| 3. Return Y_m |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCTR(N, K, T*, ICB, X) |
|-------------------------------------------------------------------|
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| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initial counter block ICB, |
| - X = X_1 | ... | X_b, X_i in V_n for i = 1, ... , b-1 and |
| X_b in V_r, where r <= n. |
| Output: |
| - Y in V_{|X|}. |
|-------------------------------------------------------------------|
| 1. If X in V_0 then return Y, where Y in V_0 |
| 2. GCTR_1 = ICB |
| 3. For i = 2, ... , b do |
| GCTR_i = Inc_c(GCTR_{i-1}) |
| 4. l = ceil(b*n / N) |
| 5. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 6. For j = 1, ... , b do |
| i = ceil(j*n / N), |
| G_j = E_{K^i}(GCTR_j) |
| 7. Y = X (xor) MSB_{|X|}(G_1 | ... | G_b) |
| 8. Return Y |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCM-ACPKM-Master-Encrypt(N, K, T*, IV, P, A) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initial counter nonce ICN in V_{n-c}, |
| - plaintext P, |P| <= n*(2^{c-1} - 2). |
| - additional authenticated data A. |
| Output: |
| - Ciphertext C, |
| - authentication tag T. |
|-------------------------------------------------------------------|
| 1. K^1 = ACPKM-Master(T*, K, k) |
| 2. H = E_{K^1}(0^n) |
| 3. If c = 32, then ICB_0 = ICN | 0^31 | 1 |
| if c!= 32, then s = n*ceil(|ICN|/n) - |ICN|, |
| ICB_0 = GHASH(ICN | 0^{s+n-64} | Vec_64(|ICN|), H) |
| 4. C = GCTR(N, K, T*, Inc_32(J_0), P) |
| 5. u = n*ceil(|C| / n) - |C| |
| v = n*ceil(|A| / n) - |A| |
| 6. S = GHASH(A | 0^v | C | 0^u | 0^{n-128} | Vec_64(|A|) | |
| | Vec_64(|C|), H) |
| 7. T = MSB_t(E_{K^1}(J_0) (xor) S) |
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| 8. Return C | T |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| GCM-ACPKM-Master-Decrypt(N, K, T*, IV, A, C, T) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initial counter nonce ICN in V_{n-c}, |
| - additional authenticated data A. |
| - ciphertext C, |C| <= n*(2^{c-1} - 2), |
| - authentication tag T, |
| Output: |
| - Plaintext P or FAIL. |
|-------------------------------------------------------------------|
| 1. K^1 = ACPKM-Master(T*, K, k) |
| 2. H = E_{K^1}(0^n) |
| 3. If c = 32, then ICB_0 = ICN | 0^31 | 1 |
| if c!= 32, then s = n*ceil(|ICN| / n) - |ICN|, |
| ICB_0 = GHASH(ICN | 0^{s+n-64} | Vec_64(|ICN|), H) |
| 4. P = GCTR(N, K, T*, Inc_32(J_0), C) |
| 5. u = n*ceil(|C| / n) - |C| |
| v = n*ceil(|A| / n) - |A| |
| 6. S = GHASH(A | 0^v | C | 0^u | 0^{n-128} | Vec_64(|A|) | |
| | Vec_64(|C|), H) |
| 7. T' = MSB_t(E_{K^1}(ICB_0) (xor) S) |
| 8. IF T = T' then return P; else return FAIL. |
+-------------------------------------------------------------------+
The * operation on (pairs of) the 2^n possible blocks corresponds to
the multiplication operation for the binary Galois (finite) field of
2^n elements defined by the polynomial f as follows (by analogy with
[GCM]):
n = 128: f = a^128 + a^7 + a^2 + a^1 + 1.
n = 256: f = a^256 + a^10 + a^5 + a^2 + 1.
The initial vector IV value for each message that is encrypted under
the given key must be chosen in a unique manner.
The message size m MUST NOT exceed (2^{n/2-1}*n*N / k) bits.
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5.2.4. CBC Mode Key Meshing
This section defines a CBC-ACPKM-Master encryption mode that uses
internal ACPKM-Master re-keying mechanism for the periodical key
transformation.
The CBC-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic encryption
mode CBC (see [MODES]).
The CBC-ACPKM-Master encryption mode can be used with the following
parameters:
o 64 <= n <= 512;
o 128 <= k <= 512.
In the specification of the CBC-ACPKM-Master mode the plaintext and
ciphertext must be a sequence of one or more complete data blocks.
If the data string to be encrypted does not initially satisfy this
property, then it MUST be padded to form complete data blocks. The
padding methods are outside the scope of this document. An example
of a padding method can be found in Appendix A of [MODES].
The key material K[j] that is used for one section processing is
equal to K^j, |K^j| = k bits.
We will denote by D_{K} the decryption function which is a
permutation inverse to the E_{K}.
The CBC-ACPKM-Master mode encryption and decryption procedures are
defined as follows:
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+----------------------------------------------------------------+
| CBC-ACPKM-Master-Encrypt(N, K, T*, IV, P) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - plaintext P = P_1 | ... | P_b, |P| <= 2^{n/2-1}*n*N / k, |
| |P_b| = n. |
| Output: |
| - Ciphertext C. |
|----------------------------------------------------------------|
| 1. l = ceil(b*n/N) |
| 2. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 3. C_0 = IV |
| 4. For j = 1, 2, ... , b do |
| i = ceil(j*n / N), |
| C_j = E_{K^i}(P_j (xor) C_{j-1}) |
| 5. Return C = C_1 | ... | C_b |
|----------------------------------------------------------------+
+----------------------------------------------------------------+
| CBC-ACPKM-Master-Decrypt(N, K, T*, IV, C) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - ciphertext C = C_1 | ... | C_b, |C| <= 2^{n/2-1}*n*N/k, |
| |C_b| = n. |
| Output: |
| - Plaintext P. |
|----------------------------------------------------------------|
| 1. l = ceil(b*n / N) |
| 2. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 3. C_0 = IV |
| 4. For j = 1, 2, ... , b do |
| i = ceil(j*n/N) |
| P_j = D_{K^i}(C_j) (xor) C_{j-1} |
| 5. Return P = P_1 | ... | P_b |
+----------------------------------------------------------------+
The initialization vector IV for each message that is encrypted under
the given key need not to be secret, but must be unpredictable.
The message size m MUST NOT exceed (2^{n/2-1}*n*N / k) bits.
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5.2.5. CFB Mode Key Meshing
This section defines a CFB-ACPKM-Master encryption mode that uses
internal ACPKM-Master re-keying mechanism for the periodical key
transformation.
The CFB-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic encryption
mode CFB (see [MODES]).
The CFB-ACPKM-Master encryption mode can be used with the following
parameters:
o 64 <= n <= 512;
o 128 <= k <= 512.
The key material K[j] that is used for one section processing is
equal to K^j, |K^j| = k bits.
The CFB-ACPKM-Master mode encryption and decryption procedures are
defined as follows:
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+-------------------------------------------------------------+
| CFB-ACPKM-Master-Encrypt(N, K, T*, IV, P) |
|-------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - plaintext P = P_1 | ... | P_b, |P| <= 2^{n/2-1}*n*N / k. |
| Output: |
| - Ciphertext C. |
|-------------------------------------------------------------|
| 1. l = ceil(b*n / N) |
| 2. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 3. C_0 = IV |
| 4. For j = 1, 2, ... , b do |
| i = ceil(j*n / N) |
| C_j = E_{K^i}(C_{j-1}) (xor) P_j |
| 5. Return C = C_1 | ... | C_b. |
|-------------------------------------------------------------+
+-------------------------------------------------------------+
| CFB-ACPKM-Master-Decrypt(N, K, T*, IV, C#) |
|-------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - ciphertext C = C_1 | ... | C_b, |C| <= 2^{n/2-1}*n*N / k.|
| Output: |
| - Plaintext P. |
|-------------------------------------------------------------|
| 1. l = ceil(b*n / N) |
| 2. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 3. C_0 = IV |
| 4. For j = 1, 2, ... , b do |
| i = ceil(j*n / N), |
| P_j = E_{K^i}(C_{j-1}) (xor) C_j |
| 5. Return P = P_1 | ... | P_b |
+-------------------------------------------------------------+
The initialization vector IV for each message that is encrypted under
the given key need not to be secret, but must be unpredictable.
The message size m MUST NOT exceed 2^{n/2-1}*n*N/k bits.
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5.2.6. OFB Mode Key Meshing
This section defines an OFB-ACPKM-Master encryption mode that uses
internal ACPKM-Master re-keying mechanism for the periodical key
transformation.
The OFB-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic encryption
mode OFB (see [MODES]).
The OFB-ACPKM-Master encryption mode can be used with the following
parameters:
o 64 <= n <= 512;
o 128 <= k <= 512.
The key material K[j] used for one section processing is equal to
K^j, |K^j| = k bits.
The OFB-ACPKM-Master mode encryption and decryption procedures are
defined as follows:
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+----------------------------------------------------------------+
| OFB-ACPKM-Master-Encrypt(N, K, T*, IV, P) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - plaintext P = P_1 | ... | P_b, |P| <= 2^{n/2-1}*n*N / k. |
| Output: |
| - Ciphertext C. |
|----------------------------------------------------------------|
| 1. l = ceil(b*n / N) |
| 2. K^1 | ... | K^l = ACPKM-Master(T*, K, k*l) |
| 3. G_0 = IV |
| 4. For j = 1, 2, ... , b do |
| i = ceil(j*n / N), |
| G_j = E_{K_i}(G_{j-1}) |
| 5. Return C = P (xor) MSB_{|P|}(G_1 | ... | G_b) |
|----------------------------------------------------------------+
+----------------------------------------------------------------+
| OFB-ACPKM-Master-Decrypt(N, K, T*, IV, C) |
|----------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - change frequency T*, |
| - initialization vector IV in V_n, |
| - ciphertext C = C_1 | ... | C_b, |C| <= 2^{n/2-1}*n*N / k. |
| Output: |
| - Plaintext P. |
|----------------------------------------------------------------|
| 1. Return OFB-ACPKM-Master-Encrypt(N, K, T*, IV, C) |
+----------------------------------------------------------------+
The initialization vector IV for each message that is encrypted under
the given key need not be unpredictable, but it must be a nonce that
is unique to each execution of the encryption operation.
The message size m MUST NOT exceed 2^{n/2-1}*n*N / k bits.
5.2.7. OMAC Mode Key Meshing
This section defines an OMAC-ACPKM-Master message authentication code
calculation mode that uses internal ACPKM-Master re-keying mechanism
for the periodical key transformation.
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The OMAC-ACPKM-Master encryption mode can be considered as the
extended by the ACPKM-Master re-keying mechanism basic message
authentication code calculation mode OMAC, which is also known as
CMAC (see [RFC4493]).
The OMAC-ACPKM-Master message authentication code calculation mode
can be used with the following parameters:
o n in {64, 128, 256};
o 128 <= k <= 512.
The key material K[j] that is used for one section processing is
equal to K^j | K^j_1, where |K^j| = k and |K^j_1| = n.
The following is a specification of the subkey generation process of
OMAC:
+-------------------------------------------------------------------+
| Generate_Subkey(K1, r) |
|-------------------------------------------------------------------|
| Input: |
| - Key K1, |
| Output: |
| - Key SK. |
|-------------------------------------------------------------------|
| 1. If r = n then return K1 |
| 2. If r < n then |
| if MSB_1(K1) = 0 |
| return K1 << 1 |
| else |
| return (K1 << 1) (xor) R_n |
| |
+-------------------------------------------------------------------+
Where R_n takes the following values:
o n = 64: R_{64} = 0^{59} | 11011;
o n = 128: R_{128} = 0^{120} | 10000111;
o n = 256: R_{256} = 0^{145} | 10000100101.
The OMAC-ACPKM-Master message authentication code calculation mode is
defined as follows:
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+-------------------------------------------------------------------+
| OMAC-ACPKM-Master(K, N, T*, M) |
|-------------------------------------------------------------------|
| Input: |
| - Section size N, |
| - master key K, |
| - key frequency T*, |
| - plaintext M = M_1 | ... | M_b, |M| <= 2^{n/2}*n^2*N / (k + n). |
| Output: |
| - message authentication code T. |
|-------------------------------------------------------------------|
| 1. C_0 = 0^n |
| 2. l = ceil(b*n / N) |
| 3. K^1 | K^1_1 | ... | K^l | K^l_1 = ACPKM-Master(T*, K, (k+n)*l |
| 4. For j = 1, 2, ... , b-1 do |
| i = ceil(j*n / N), |
| C_j = E_{K^i}(M_j (xor) C_{j-1}) |
| 5. SK = Generate_Subkey(K^l_1, |M_b|) |
| 6. If |M_b| = n then M*_b = M_b |
| else M*_b = M_b | 1 | 0^{n - 1 -|M_b|} |
| 7. T = E_{K^l}(M*_b (xor) C_{b-1} (xor) SK) |
| 8. Return T |
+-------------------------------------------------------------------+
The message size m MUST NOT exceed 2^{n/2}*n^2*N / (k + n) bits.
6. Joint Usage of External and Internal Re-keying
Any mechanism described in Section 4 can be used with any mechanism
described in Section 5.
7. Scope of Usage of Rekeying-Based Schemas
7.1. Key Transformation Rules
External re-keying mechanisms increase the number of messages that
can be processed with one negotiated key.
The key K^i (see Figure 1 and Figure 2) can be transformed in
accordance with one of the following two approaches:
o Explicit approach:
|M^{i,1}| + ... + |M^{i,q_i}| <= L, |M^{i,1}| + ... + |M^{i,q_i +
1}| > L, i = 1, ... , t.
This approach allows to use the key K^i in almost optimal way but
it cannot be applied in case when messages may be lost or
reordered (e.g. DTLS packets).
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o Implicit approach:
q_i = L / m_max, i = 1, ... , t.
The amount of data processed with one key K^i is calculated under
the assumption that every message has the maximum length m_max.
Hence this amount can be considerably less than the key lifetime
limitation L. On the other hand this approach can be applied in
case when messages may be lost or reordered (e.g. DTLS packets).
Internal re-keying mechanisms increase the length of messages that
can be processed with one negotiated key.
The key K (see Figure 3 and Figure 4) can be updated in accordance
with one of the following two approaches:
o Explicit approach:
|M^{1}_1| + ... + |M^{q}_1| <= L, |M^{1}_1| + ... + |M^{q+1}_1| >
L (where M^{i}_1 is the first section of message M^{i}, i = 1, ...
, q).
This approach allows to use the key K^i in almost optimal way but
it cannot be applied in case messages data may be lost or
reordered (e.g. DTLS packets).
o Implicit approach:
q = L / N.
The amount of data processed with one key K^i is calculated under
the assumption that the length of every message is equal or more
then section size N and so it can be considerably less than the
key lifetime limitation L. On the other hand this approach can be
applied in case when messages may be lost or reordered (e.g. DTLS
packets).
7.2. Principles of Choice of Constructions and Security Parameters
External re-keying mechanism is recommended to be used in protocols
that process pretty small messages (e.g. TLS records are 2^14 bytes
or less).
Consider an example. Let the message size in some protocol P be
equal to 1 KB (m_max = 1 KB). Suppose a cipher E is used for
encrypting and L1 = 128 MB is the key lifetime limitation induced by
side channels analysis methods. Let the key lifetime limitation L2
induced by the analysis of encryption mode used in this protocol be
equal to 1 TB. The most restrictive resulting key lifetime
limitation is equal to 128 MB.
Thus, if external re-keying mechanism is not used, the key K must be
renegotiated after processing 128 MB / 1 KB = 131072 messages.
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If an external re-keying mechanism with parameter L = 64 MB (see
Section 7.1 ) that limits the amount of data processed with one key
K^i is used, the key lifetime limitation L1 induced by the side
channels analysis methods goes off. Thus the resulting key lifetime
limitation of the negotiated key K can be calculated on the basis of
the used encryption mode analysis. It is proven that the security of
the encryption mode that uses external re-keying leads to an increase
when compared to base encryption mode without re-keying (see
[AbBell]). Hence the resulting key lifetime limitation in case of
using external re-keying is equal to 1 TB.
Thus if an external re-keying mechanism is used, then 1 TB / 1 KB =
2^30 messages can be processed before the key K is renegotiated,
which is 8192 times greater than the number of messages that can be
processed, when external re-keying mechanism is not used.
An internal re-keying mechanism is recommended to be used in
protocols that can process large single messages (e.g. CMS
messages).
Since the performance of encryption can slightly decrease for rather
small values of N, the parameter N should be selected for a
particular protocol as maximum possible to provide necessary key
lifetime for the adversary models that are considered.
Consider an example. Let the message size in some protocol P' is
large/unlimited. Suppose a cipher E is used for encrypting and L1 =
128 MB is the most restrictive key lifetime limitation induced by the
side channels analysis methods.
Thus, there is a need to put a limit on maximum message size m_max.
For example, if m_max = 32 MB, it may happen that the renegotiation
of key K would be required after processing only four messages.
If an internal re-keying mechanism with section size N = 1 MB (see
Figure 3 and Figure 4) is used, maximum message size limit m_max can
be increased to hundreds of terabytes and L / N = 128 MB / 1 MB = 128
messages can be processed before the renegotiation of key K (instead
of 4 messages in case when an internal re-keying mechanism is not
used).
For the protocols that process messages of different lengths it is
recommended to use joint methods (see Section 6).
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8. Security Considerations
Re-keying should be used to increase "a priori" security properties
of ciphers in hostile environments (e.g. with side-channel
adversaries). If some non-negligible attacks are known for a cipher,
it must not be used. So re-keying cannot be used as a patch for
vulnerable ciphers. Base cipher properties must be well analyzed,
because security of re-keying mechanisms is based on security of a
block cipher as a pseudorandom function.
The key lifetime limitation can be subject to the following
considerations:
1. Methods of analysis based on the used encryption mode properties.
* These methods do not depend on the used block cipher
permutation E_{K}.
* For standard encryption modes this restriction has the order
2^{n/2}.
2. Methods based on the side channels analysis.
* These methods do not depend on the used encryption modes.
* These methods are weakly dependent on the used block cipher
features (only the way of elementary internal transformation
that uses key material matter, in most cases this is (xor)).
* Restrictions resulting from these methods are usually the
strongest ones.
3. Methods based on the properties of the used block cipher
permutation E_{K} (for example, linear or differential
cryptanalysis).
* In most cases these methods do not depend on the used
encryption modes.
* In case of secure block ciphers restrictions resulting from
such methods are roughly the same as the natural limitation
2^n.
9. References
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9.1. Normative References
[GCM] McGrew, D. and J. Viega, "The Galois/Counter Mode of
Operation (GCM)", Submission to NIST
http://csrc.nist.gov/CryptoToolkit/modes/proposedmodes/
gcm/gcm-spec.pdf, January 2004.
[GOST3411-2012]
Federal Agency on Technical Regulating and Metrology (In
Russian), "Information technology. Cryptographic Data
Security. Hashing function", GOST R 34.11-2012, 2012.
[MODES] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Methods and Techniques", NIST Special
Publication 800-38A, December 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
2006, <http://www.rfc-editor.org/info/rfc4493>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<http://www.rfc-editor.org/info/rfc5869>.
[SHA-512] National Institute of Standards and Technology., "Secure
Hash Standard", FIPS 180-2, August, with Change Notice 1
dated February 2004 2002.
[TLSDraft]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", 2017, <https://tools.ietf.org/html/draft-
ietf-tls-tls13-18>.
9.2. Informative References
[AbBell] Michel Abdalla and Mihir Bellare, "Increasing the Lifetime
of a Key: A Comparative Analysis of the Security of Re-
keying Techniques", ASIACRYPT2000, LNCS 1976, pp. 546-559,
2000.
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[BDJR] Bellare M., Desai A., Jokipii E., Rogaway P., "A concrete
security treatment of symmetric encryption", In
Proceedings of 38th Annual Symposium on Foundations of
Computer Science (FOCS '97), pages 394-403. 97, 1997.
[BL] Bhargavan K., Leurent G., "On the Practical (In-)Security
of 64-bit Block Ciphers: Collision Attacks on HTTP over
TLS and OpenVPN", Cryptology ePrint Archive Report 798,
2016.
[Matsui] Matsui M., "Linear Cryptanalysis Method for DES Cipher",
Advanced in Cryptology- EUROCRYPT'93. Lect. Notes in Comp.
Sci., Springer. V.765.P. 386-397, 1994.
[RFC6986] Dolmatov, V., Ed. and A. Degtyarev, "GOST R 34.11-2012:
Hash Function", RFC 6986, DOI 10.17487/RFC6986, August
2013, <http://www.rfc-editor.org/info/rfc6986>.
Appendix A. Test examples
CTR-ACPKM mode with AES-256
*********
c = 64
k = 256
N = 256
n = 128
W_0:
F3 74 E9 23 FE AA D6 DD 98 B4 B6 3D 57 8B 35 AC
W_1:
A9 0F D7 31 E4 1D 64 5E C0 8C 87 87 28 CC 76 90
Key K:
88 99 AA BB CC DD EE FF 00 11 22 33 44 55 66 77
FE DC BA 98 76 54 32 10 01 23 45 67 89 AB CD EF
Plain text P:
11 22 33 44 55 66 77 00 FF EE DD CC BB AA 99 88
00 11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A
11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00
22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 11
33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 11 22
44 55 66 77 88 99 AA BB CC EE FF 0A 00 11 22 33
55 66 77 88 99 AA BB CC EE FF 0A 00 11 22 33 44
ICN:
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12 34 56 78 90 AB CE F0
ACPKM's iteration 1
Process block 1
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 00
Output block (ctr)
FD 7E F8 9A D9 7E A4 B8 8D B8 B5 1C 1C 9D 6D D0
Plain text
11 22 33 44 55 66 77 00 FF EE DD CC BB AA 99 88
Cipher text
EC 5C CB DE 8C 18 D3 B8 72 56 68 D0 A7 37 F4 58
Process block 2
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 01
Output block (ctr)
19 98 C5 71 76 37 FB 17 11 E4 48 F0 0C 0D 60 B2
Plain text
00 11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A
Cipher text
19 89 E7 42 32 62 9D 60 99 7D E2 4B C0 E3 9F B8
Updated key
C6 C1 AF 82 3F 52 22 F8 97 CF F1 94 5D F7 21 9E
21 6F 29 0C EF C4 C7 E6 DC C8 B7 DD 83 E0 AE 60
ACPKM's iteration 2
Process block 3
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 02
Output block (ctr)
92 B4 85 B5 B7 AD 3C 19 7E 53 92 32 13 9C 8E 7A
Plain text
11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00
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Cipher text
83 96 B6 F1 E2 CB 4B 91 E7 F9 29 FE FD 63 84 7A
Process block 4
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 03
Output block (ctr)
59 3A AA 96 7C E3 58 FB 1B 7E 41 A1 77 34 B1 4A
Plain text
22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 11
Cipher text
7B 09 EE C3 1A 94 D0 62 B1 C5 8D 4F 88 3E B1 5B
Updated key
65 3E FA 18 0B 0E 68 01 6F 56 54 A5 F3 EE BC D5
04 F1 1F E3 F1 7A 92 07 57 A8 82 BE A5 9E CA 16
ACPKM's iteration 3
Process block 5
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 04
Output block (ctr)
CE E5 51 54 12 2F 3F E7 8D 8E 86 21 C5 E5 47 12
Plain text
33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 11 22
Cipher text
FD A1 04 32 65 A7 A6 4D 36 42 68 DE CF E5 56 30
Process block 6
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 05
Output block (ctr)
DE D6 8F 03 FA C5 C5 B6 16 11 A3 78 2C 0D C1 EB
Plain text
44 55 66 77 88 99 AA BB CC EE FF 0A 00 11 22 33
Cipher text
9A 83 E9 74 72 5C 6F 0D DA FF 5C 72 2C 1C E3 D8
Updated key
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C0 D5 50 26 4F DA CE 59 EF 80 9A 50 24 72 06 7D
29 83 74 25 78 C9 60 4F E3 B8 88 4F F8 F5 E2 BD
ACPKM's iteration 4
Process block 7
Input block (ctr)
12 34 56 78 90 AB CE F0 00 00 00 00 00 00 00 06
Output block (ctr)
D9 23 A6 CD 8A 00 A1 55 90 09 EC 87 40 B9 D6 AB
Plain text
55 66 77 88 99 AA BB CC EE FF 0A 00 11 22 33 44
Cipher text
8C 45 D1 45 13 AA 1A 99 7E F6 E6 87 51 9B E5 EF
Updated key
6A A0 92 07 73 31 63 50 46 FA 48 1C 9C 98 7B 6B
FC 99 48 DC BC AE AB C2 6D 46 E9 DD 43 F6 CA 56
Encrypted src
EC 5C CB DE 8C 18 D3 B8 72 56 68 D0 A7 37 F4 58
19 89 E7 42 32 62 9D 60 99 7D E2 4B C0 E3 9F B8
83 96 B6 F1 E2 CB 4B 91 E7 F9 29 FE FD 63 84 7A
7B 09 EE C3 1A 94 D0 62 B1 C5 8D 4F 88 3E B1 5B
FD A1 04 32 65 A7 A6 4D 36 42 68 DE CF E5 56 30
9A 83 E9 74 72 5C 6F 0D DA FF 5C 72 2C 1C E3 D8
8C 45 D1 45 13 AA 1A 99 7E F6 E6 87 51 9B E5 EF
Appendix B. Contributors
o Daniel Fox Franke
Akamai Technologies
dfoxfranke@gmail.com
o Lilia Ahmetzyanova
CryptoPro
lah@cryptopro.ru
o Ruth Ng
University of California, San Diego
ring@eng.ucsd.edu
o Shay Gueron
University of Haifa, Israel
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Intel Corporation, Israel Development Center, Israel
shay.gueron@gmail.com
Authors' Addresses
Stanislav Smyshlyaev (editor)
CryptoPro
18, Suschevsky val
Moscow 127018
Russian Federation
Phone: +7 (495) 995-48-20
Email: svs@cryptopro.ru
Russ Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon VA 20170
USA
Email: housley@vigilsec.com
Mihir Bellare
University of California, San Diego
9500 Gilman Drive
La Jolla California 92093-0404
USA
Phone: (858) 534-4544
Email: mihir@eng.ucsd.edu
Evgeny Alekseev
CryptoPro
18, Suschevsky val
Moscow 127018
Russian Federation
Phone: +7 (495) 995-48-20
Email: alekseev@cryptopro.ru
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Ekaterina Smyshlyaeva
CryptoPro
18, Suschevsky val
Moscow 127018
Russian Federation
Phone: +7 (495) 995-48-20
Email: ess@cryptopro.ru
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