DNS Extensions S. Krishnaswamy
Internet-Draft A. Hayatnagarkar
Intended status: Informational SPARTA, Inc.
Expires: April 24, 2007 October 21, 2006
DNSSEC Validator API
draft-hayatnagarkar-dnsext-validator-api-02
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The DNS Security Extensions (DNSSEC) provide origin authentication
and integrity of DNS data. However, the current resolver Application
Programming Interface (API) does not allow a security-aware resolver
to communicate detailed results of DNSSEC processing back to the
application. This document describes an API between applications and
a validating security-aware stub resolver that allows applications to
control the validation process and obtain results of DNSSEC
processing.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. High-level Validator API . . . . . . . . . . . . . . . . . . . 4
3.1. val_gethostbyname, val_gethostbyname_r,
val_gethostbyaddr, val_gethostbyaddr_r . . . . . . . . . . 5
3.2. val_getaddrinfo, val_getnameinfo, val_freeaddrinfo . . . . 7
3.3. val_query, val_res_query . . . . . . . . . . . . . . . . . 8
3.4. p_val_error . . . . . . . . . . . . . . . . . . . . . . . 9
4. Low-level Validator API . . . . . . . . . . . . . . . . . . . 10
4.1. val_resolve_and_check, val_free_result_chain,
p_as_error . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Assertion Status Codes . . . . . . . . . . . . . . . . . . 13
5. Context Management and Validator Policy API . . . . . . . . . 17
5.1. val_create_context, val_free_context . . . . . . . . . . . 18
5.2. val_get_policy_definition, val_set_policy_definition . . . 19
6. Validation Status Codes and Return Values . . . . . . . . . . 19
6.1. Return Values . . . . . . . . . . . . . . . . . . . . . . 19
6.2. Validation Status Codes . . . . . . . . . . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . . . 24
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1. Introduction
The DNS Security Extensions (RFC 4033 [2], RFC 4034 [3], RFC 4035
[4]) allow resolvers to test the origin authenticity and integrity of
data returned by the DNS. A validator, or more formally, a
validating security-aware stub resolver, is a piece of software that
performs these tests by checking the cryptographic signatures that
cover DNS records and by verifying a sequence of such records from a
trust anchor [2] to these signed records. This document presents an
API between an application and a validator, which provides a
convenient way for applications to control the DNSSEC validation
process and obtain detailed validation results on which to base
program behavior.
The API can be broadly divided into three groups: the high-Level
validator API, the low-Level validator API and the context management
API.
The high-level validator API is designed for ease of use and mirrors
existing DNS-related functions. This API is best suited for existing
applications that already use legacy DNS-related functions such as
gethostbyname(), getaddrinfo() and res_query() and have no
requirement for detailed validation status information.
The low-level validator API allows detailed inspection of validation
status for each element of the authentication chain [2].
Validator operation can be guided by local policy. The context
management API provides functions for applications to control which
policies are used during DNSSEC validation.
The range of functions provided in this API allows for the creation
of applications that are either only interested in basic results such
as "validated" or "not-validated", or more sophisticated applications
that can look for specific errors in the authentication chain as a
sign of a network abnormality or attack.
Section 3, Section 4, and Section 5 describe these interfaces in
greater detail.
2. Terminology
Some of the terms used in this specification are defined below:
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legacy functions: Functions such as gethostbyname() and
getaddrinfo() that are not capable of returning validation status
values for DNS responses and are typically used by DNSSEC-unaware
applications.
validator policy: a set of configuration parameters for the
validator that can influence the eventual outcome of the
validation process.
policy attribute: a particular configurable component of the
validator policy; for instance a trust anchor setting or an
untrusted algorithm definition.
validator context: an opaque structure encapsulating the validator
policy. The validator context is the application's handle to the
validator policy.
active policy: the policy definition that is associated with a
validator context.
default policy: the policy definition that is used by the validator
when the application does not specify its own preference while
creating a validator context.
3. High-level Validator API
The high-level validator API provides DNSSEC-aware substitutes for
commonly used DNS functions such as gethostbyname(), getaddrinfo(),
and res_query(). This API provides an easy path for applications
already using these legacy functions to transition towards becoming
DNSSEC-aware.
The ctx parameter used in the following functions points to the
validator context. An application may explicitly create a context
using the val_create_context() function described in Section 5, or
allow the API to create one internally by specifying the value of
NULL for the ctx parameter.
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3.1. val_gethostbyname, val_gethostbyname_r, val_gethostbyaddr,
val_gethostbyaddr_r
struct hostent *val_gethostbyname( const val_context_t *ctx,
const char *name,
val_status_t *val_status );
int val_gethostbyname_r( const val_context_t *ctx,
const char *name,
struct hostent *ret,
char *buf,
size_t buflen,
struct hostent **result,
int *h_errnop,
val_status_t *val_status );
struct hostent *val_gethostbyaddr( const val_context_t *ctx,
const char *addr,
int len,
int type,
val_status_t *val_status );
int val_gethostbyaddr_r( const val_context_t *ctx,
const char *addr,
int len,
int type,
struct hostent *ret,
char *buf,
int buflen,
struct hostent **result,
int *h_errnop,
val_status_t *val_status );
The val_gethostbyname(), val_gethostbyname_r(), val_gethostbyaddr()
and val_gethostbyaddr_r() functions are DNSSEC-aware versions of the
gethostbyname(), gethostbyname_r(), gethostbyaddr() and
gethostbyaddr_r() legacy functions that perform name-to-address and
address-to-name translations and also return the validation status of
DNS responses. These functions must be only used when retrofitting
DNSSEC in applications that use the legacy functions. For other
applications, it is instead recommended to use the replacement
functions from Section 3.2 to perform address-to-name and name-to-
address translations.
The val_gethostbyname() function returns a pointer to a structure of
type hostent for the host name provided in name. The name can also
be an IPv4 address in standard dot notation, or an IPv6 address in
colon (and possibly dot) notation. If name is an IPv4 or IPv6
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address, no lookup is performed and val_gethostbyname() simply copies
name into the h_name field and its struct in-addr equivalent into the
h_addr_list[0] of the returned hostnet structure.
The val_gethostbyaddr() function returns a pointer to a structure of
type hostent for the given host address addr whose length is given by
the len parameter and address type is given by the type parameter.
Valid address types are AF_INET and AF_INET6.
As with gethostbyname() and gethostbyaddr(), the val_gethostbyname()
and val_gethostbyaddr() functions set the value of the global h_errno
variable. These functions return a pointer to a struct hostent value
on success, and NULL on error. Their return values may point to
static data, and may be overwritten by subsequent calls. Making a
simple copy of struct hostent is not sufficient since the structure
contains pointers - a deep copy is required.
The val_gethostbyname_r() and val_gethostbyaddr_r() functions are
reentrant and thread-safe versions of the val_gethostbyname() and
val_gethostbyaddr() functions. These functions return 0 on success,
and a non-zero value on error. The result of the call is stored in
the ret parameter. These functions do not modify the global h_errno
variable, but return the error numbers in the h_errnop parameter.
After the call, the value of result will be NULL on error or point to
the ret paramter on success. Auxiliary data is stored in the buffer
buf of length buflen. If the buffer is too small, these functions
will return the error ERANGE.
The val_status parameter contains the status of DNSSEC validation.
Possible values for this type are defined in Section 6.2. A
validation status of VAL_SUCCESS will be returned only if both the
address and canonical name(s) within the hostent structure, if any,
are validated successfully. The validation status value can be
displayed in a string format using the p_val_error() function as
described in Section 3.4.
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3.2. val_getaddrinfo, val_getnameinfo, val_freeaddrinfo
int val_getaddrinfo( const val_context_t *ctx,
const char *nodename,
const char *servname,
const struct addrinfo *hints,
struct val_addrinfo **res );
int val_getnameinfo( const val_context_t *ctx,
const struct sockaddr *sa,
socklen_t salen,
char *host,
size_t hostlen,
char *serv,
size_t servlen,
int flags,
val_status_t *val_status );
void val_freeaddrinfo( struct val_addrinfo *ainfo );
struct val_addrinfo {
int ai_flags;
int ai_family;
int ai_socktype;
int ai_protocol;
size_t ai_addrlen;
struct sockaddr *ai_addr;
char *ai_canonname;
struct val_addrinfo *ai_next;
val_status_t ai_val_status;
}
The val_getaddrinfo() function returns the address and service
information for the specified domain name and service. It is a
DNSSEC-aware version of the getaddrinfo() legacy function (RFC 3493
[1]). This function supports both IPv4 and IPv6 addresses. It
returns a pointer to a value of type val_addrinfo in the value of the
res field on success, and NULL on error. The val_addrinfo structure
is an augmented form of the addrinfo structure. It contains an
additional ai_val_status field that represents the status of DNSSEC
validation for that particular answer. The memory for the value of
res is dynamically allocated by this function and the caller should
release it after use with the val_freeaddrinfo() function. The
syntax and semantics of other parameters in val_getaddrinfo() are
identical to that specified in [1].
The val_getnameinfo() function performs an address-to-name
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translation in a protocol independent manner. It is a DNSSEC-aware
version of the getnameinfo() legacy function (RFC 3493 [1]). In
addition to the values returned by the getnameinfo() function, this
function returns the DNSSEC validation status in the val_status
parameter. The syntax and semantics of other parameters in
val_getnameinfo() are identical to that specified in [1].
val_status contains a validation status of VAL_SUCCESS only if both
the address and canonical name within the val_addrinfo structure, if
present, are validated successfully. The validation status value can
be displayed in a string format using the p_val_error() function as
described in Section 3.4.
The val_getaddrinfo() and val_getnameinfo() functions return 0 on
success and a non-zero value on error.
3.3. val_query, val_res_query
int val_query( const val_context_t *ctx,
const char *domain_name,
const u_int16_t class,
const u_int16_t type,
const u_int8_t flags,
struct val_response **resp);
int val_free_response(struct val_response *resp);
int val_res_query(const val_context_t *ctx,
const char *domain_name,
int class,
int type,
u_char *answer,
int anslen,
val_status_t *val_status);
struct val_response {
unsigned char *vr_response;
int vr_length;
val_status_t vr_val_status;
struct val_response *vr_next;
};
The val_query() and val_res_query() functions query the name server
for the fully qualified domain name present in the domain_name field
of the given class and type. In addition to the answers to the
query, they return the status of DNSSEC validation. They are
intended as DNSSEC-aware replacements for the res_query() function.
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val_query() is provided to return the individual validation status
values for multiple RRsets returned in response to a query. Multiple
RRsets may be returned if the query type is ANY or RRSIG. The memory
for the value of resp is internally allocated and must be released
after a successful invocation of val_query() using the
val_free_response() function.
The val_query() function returns 0 on success and a non-zero error
code on failure. On success, the memory pointed to by resp contains
a linked-list of responses returned by the validator. By default,
each val_response structure in the linked-list within resp holds a
single RRset response. The format of the vr_response field within
the val_response structure is similar to the format of the answer
returned by res_query() and is of length vr_length. The
vr_val_status field contains the status of DNSSEC validation for that
particular RRset and may be displayed in a string format using the
p_val_error() function as described in Section 3.4. Elements within
the resp linked-list may be accessed by traversing the list using the
vr_next field.
The flags parameter controls the scope of validation and the output
format. Only the VAL_QUERY_MERGE_RRSETS flag is currently defined.
When this flag is specified, all RRsets in the answer are merged into
a single response and returned in the first (and only) element of the
resp linked list. The vr_response field of this element will have a
format similar to the answer returned by res_query(). The validation
status will be VAL_SUCCESS only if all the individual RRsets are
trusted. If this flag is used and a value other than VAL_SUCCESS is
returned with multiple RRsets in the answer, it will not be possible
to know which RRset resulted in the error status.
The val_res_query() function is semantically closer to the
res_query(3) function than val_query(). It internally invokes the
val_query() function supplying it with the VAL_QUERY_MERGE_RRSETS
flag and returns the final response in the answer field. The number
of bytes available in the answer field is returned in the anslen
field. The val_res_query() function returns the value of anslen on
success and -1 on failure.
3.4. p_val_error
char *p_val_error(val_status_t err);
The p_val_error() function can be used to display the validation
status information contained in the parameter with type val_status_t
in a string format. The returned values are string representations
of the definitions given in Section 6.2.
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4. Low-level Validator API
The low-level validator API provides the application with greater
control and visibility into the validation process. The functions
and data structures defined in the low-level validator API are
summarized below.
4.1. val_resolve_and_check, val_free_result_chain, p_as_error
int val_resolve_and_check( const val_context_t *context,
const char *domain_name,
const u_int16_t class,
const u_int16_t type,
const u_int8_t flags,
struct val_result_chain **results);
void val_free_result_chain( struct val_result_chain *results );
char *p_as_error(val_astatus_t err);
#define MAX_PROOFS 4
struct val_result_chain {
val_status_t val_rc_status;
struct val_authentication_chain *val_rc_answer;
int val_rc_proof_count;
struct val_authentication_chain *val_rc_proofs[MAX_PROOFS];
struct val_result_chain *val_rc_next;
};
struct val_authentication_chain {
val_astatus_t val_ac_status;
struct val_rrset *val_ac_rrset;
struct val_authentication_chain *val_ac_trust;
};
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struct val_rrset {
u_int8_t *val_msg_header;
u_int16_t val_msg_headerlen;
u_int8_t *val_rrset_name_n;
u_int16_t val_rrset_class_h;
u_int16_t val_rrset_type_h;
u_int32_t val_rrset_ttl_h;
u_int8_t val_rrset_section;
struct sockaddr *val_rrset_server;
struct rr_rec *val_rrset_data;
struct rr_rec *val_rrset_sig;
};
struct rr_rec {
u_int16_t rr_rdata_length_h;
u_int8_t *rr_rdata;
val_astatus rr_status;
struct rr_rec *rr_next;
};
The val_resolve_and_check() function queries a set of name servers
for the <domain_name, class, type> tuple and then verifies and
validates the responses received. The verification step checks the
RRSIGs and the validation step performs verification down the
authentication chain from a trust anchor. All the information
necessary for inspecting the authentication chain is available
through the results parameter. The context parameter points to the
validator context. An application may explicitly create a context
using the val_create_context() function described in Section 5, or
allow the validator to create one internally by specifying the value
of NULL for this parameter. Only the VAL_FLAGS_DONT_VALIDATE flag is
currently defined. This flag has the effect of turning off
validation -- no authentication chain is constructed for this
response.
val_resolve_and_check() returns 0 on success and an error code from
Section 6.1 on failure. The val_resolve_and_check() function
internally allocates memory for the value of the result parameter,
which must be released after a successful call to this function using
the val_free_result_chain() function.
Answers to the query are returned in results, which is a linked-list
of val_result_chain structures. Each element in the linked-list
corresponds to a distinct RRset returned in the answer section along
with any associated proofs of non-existence. Multiple RRs within the
RRset are all part of the same answer. Multiple answers are possible
when the query type is ANY or RRSIG. The val_rc_next field can be
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used to iterate through the list of all results returned by the
validator. The consolidated validation status value for an RRset in
the DNS response based on the individual status values for all
components in the authentication chain is stored in the val_rc_status
field, which is of type val_status_t. Possible values for this type
are listed in Section 6.2 and can be displayed in a string format
using the p_val_error() function as described in Section 3.4.
Members of the authentication chain sequence are encapsulated in the
val_authentication_chain structure, which provides greater detail
about the validation status for each component in the authentication
chain. The val_rc_answer field in the val_result_chain structure
points to the next element in the authentication chain sequence
proceeding from the signed record towards the trust anchor. The
proofs of non-existence for this query or any proofs that are
required to support the validity of information in val_rc_answer are
returned in the val_rc_proofs array. val_rc_proof_count provides the
number of elements present in this array.
Within the val_authentication_chain structure, the val_ac_status
field returns the validation status for the specified RRset.
Possible values for this field are defined in Section 4.2. These
values can be displayed in a string format using the p_as_error()
function. The val_ac_trust field points to the next element in the
authentication chain. For a element with type DNSKEY, the next
element corresponds to a DS record in the parent zone and for a DS
record the next element corresponds to the DNSKEY in the current
zone. Its value is NULL when the current element in the linked list
points to a valid trust anchor or in the case of an error, when the
next node in the authentication chain from the record to the trust
anchor cannot be constructed. The val_ac_status field can be used to
differentiate between these two cases.
The val_ac_rrset field in the val_authentication_chain structure
contains the actual RRset data. The information stored in this
structure includes the header of the DNS response in which the RRset
was received (in the val_msg_header field with length given by the
val_msg_headerlen field) and the DNS response "envelope" comprising
of the name, class, type and time-to-live tuple (in the
val_rrset_name_n, val_rrset_class_h, val_rrset_type_h and
val_rrset_ttl_h fields respectively). The name servers from where
these RRsets were received is stored in the val_rrset_server field.
The response RDATA is stored within val_rrset_data. Any RRSIGs that
are applicable to the response RDATA are stored within val_rrset_sig.
Both of these variables are of type rr_rec, which is a list of name-
value pairs corresponding to each resource-record within the RRset.
Members of the val_rrset_sig and val_rrset_data linked lists also
have rr_status fields of type val_astatus_t. This field only takes
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on a subset of all status values possible for val_astatus_t,
specifically, those pertaining to signature verification as defined
in Section 4.2).
The section where the RRset appears in the DNS response is saved in
the val_rrset_section field within the val_rrset structure and may
contain one of the following values,
VAL_FROM_ANSWER: returned if the RRset was present in the answer
section of the DNS response.
VAL_FROM_AUTHORITY: returned if the RRset was present in the
authority section of the DNS response.
VAL_FROM_ADDITIONAL: returned if the RRset was present in the
additional section of the DNS response.
4.2. Assertion Status Codes
o The verification status value stored in the val_ac_status member
of the val_authentication_chain structure can have one of the
following values:
VAL_A_UNSET: returned if the status was not set.
VAL_A_DATA_MISSING: returned if there was no data returned for a
query and the DNS did not indicate an error.
VAL_A_RRSIG_MISSING: returned if RRSIG data could not be
retrieved for a resource record.
VAL_A_DNSKEY_MISSING: returned if the DNSKEY for an RRSIG
covering a resource record was not available.
VAL_A_DS_MISSING: returned if the DS record covering a DNSKEY
record was not available.
VAL_A_UNTRUSTED_ZONE: returned if local policy defined a given
zone as untrusted.
VAL_A_DNSSEC_VERSION_ERROR: returned if the DNSSEC version was
unrecognized.
VAL_A_TOO_MANY_LINKS: returned if local policy identified a given
authentication chain as being too long.
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VAL_A_UNKNOWN_DNSKEY_PROTO: returned if the DNSKEY protocol
number was unrecognized.
VAL_A_NOT_VERIFIED: returned if all RRSIGs covering the an RRset
could not be verified.
VAL_A_VERIFIED: returned if at least one RRSIG covering a
resource record had a status of VAL_A_RRSIG_VERIFIED.
VAL_A_LOCAL_ANSWER: returned if the answer was obtained locally
(for example, a file such as /etc/hosts).
VAL_A_TRUST_KEY: returned if a given DNSKEY or a DS record was
locally defined to be a trust anchor.
VAL_A_TRUST_ZONE: returned if local policy defined a given zone
as trusted.
VAL_A_PROVABLY_UNSECURE: returned if the authentication chain
from a trust anchor to a given zone could not be constructed
due to the provable absence of a DS record for this zone in the
parent.
VAL_A_BARE_RRSIG: returned if the response was for a query of
type RRSIG. RRSIGs contain the cryptographic signatures for
other DNS data and cannot themselves be validated.
VAL_A_NO_TRUST_ANCHOR: returned if there was no trust anchor
configured for a given authentication chain.
o Resolver-related status values in val_ac_status are reflected by
one of the following values, offset by the value of
VAL_A_DNS_ERROR_BASE :
SR_INTERNAL_ERROR: returned if an internal error was encountered
in the resolver.
SR_TSIG_ERROR: returned if there was an error in TSIG processing.
SR_NO_ANSWER: returned if no answer was received for a query.
SR_WRONG_ANSWER: returned if a message received was not a valid
response to a query.
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SR_HEADER_BADSIZE: returned if the message size was not
consistent with header values.
SR_NXDOMAIN: returned if rcode was set to NXDOMAIN, but either
the authority section contains data other than a proof of non-
existence or the answer and additional sections were not empty.
SR_FORMERR: returned if rcode was set to FORMERR.
SR_SERVFAIL: returned if rcode was set to SERVFAIL.
SR_NOTIMPL: returned if rcode was set to NOTIMPL.
SR_REFUSED: returned if rcode was set to REFUSED.
SR_DNS_GENERIC_ERROR: returned if the response was received with
the rcode set to one of the well-known error values namely
NXDOMAIN, FORMERR, SR_SERVFAIL, SR_NOTIMPL and SR_REFUSED.
SR_EDNS_VERSION_ERROR: returned if the EDNS0 version was not
recognized.
SR_UNSUPP_EDNS0_LABEL: returned if the EDNS0 label was not
supported.
SR_SUSPICIOUS_BIT: returned if some bit in the response headers
was unexpectedly set or unset.
SR_NAME_EXPANSION_FAILURE: returned if DNS name uncompression
failed.
SR_REFERRAL_ERROR: returned if referrals for a query could not be
successfully followed.
SR_MISSING_GLUE: returned if glue records were not available for
a referral.
SR_CONFLICTING_ANSWERS: returned if multiple answers were
returned for a query, but they were inconsistent with each
other.
o For each signature rr_rec member within the authentication chain
val_ac_rrset, the validation status stored in the variable
rr_status can return one of the following values:
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VAL_A_RRSIG_VERIFIED: returned if the RRSIG verified
successfully.
VAL_A_WCARD_VERIFIED: returned if a given RRSIG covering a
resource record shows that the record was wildcard expanded.
VAL_A_RRSIG_VERIFY_FAILED: returned if a given RRSIG covering an
RRset was bogus.
VAL_A_DNSKEY_NOMATCH: returned if an RRSIG was created by a
DNSKEY that did not exist in the apex keyset.
VAL_A_WRONG_LABEL_COUNT: returned if the number of labels on the
signature was greater than the the count given in the RRSIG
RDATA.
VAL_A_SECURITY_LAME: returned if an RRSIG was created with a key
that did not exist in the parent DS record set.
VAL_A_RRSIG_NOTYETACTIVE: returned if the RRSIG's inception time
was in the future.
VAL_A_RRSIG_EXPIRED: returned if the RRSIG had expired.
VAL_A_ALGO_NOT_SUPPORTED: returned if the RRSIG algorithm was not
supported.
VAL_A_UNKNOWN_ALGO: returned if the RRSIG algorithm was unknown.
VAL_A_ALGO_REFUSED: returned if the RRSIG algorithm was not
allowed as per local policy.
o For each rr_rec member of type DNSKEY (or DS where relevant)
within the authentication chain val_ac_rrset, the validation
status is stored in the variable rr_status can return one of the
following values:
VAL_A_SIGNING_KEY: returned if this DNSKEY was used to create an
RRSIG for the resource record set.
VAL_A_VERIFIED_LINK: returned if this DNSKEY provided the link in
the authentication chain from the trust anchor to the signed
record.
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VAL_A_UNKOWN_ALGO_LINK: returned if this DNSKEY provided the link
in the authentication chain from the trust anchor to the signed
record, but the DNSKEY algorithm was unknown.
VAL_A_INVALID_KEY: returned if the key used to verify the RRSIG
was not valid DNSKEY.
VAL_A_KEY_TOO_LARGE: returned if local policy defined the DNSKEY
size as being too large.
VAL_A_KEY_TOO_SMALL: returned if local policy defined the DNSKEY
size as being too small.
VAL_A_KEY_NOT_AUTHORIZED: returned if local policy defined the
DNSKEY to be unauthorized for validation.
VAL_A_NO_PREFERRED_SEP: returned if the parent DS record
contained a corresponding hash but local policy did not permits
the validator to build its authentication chain from this
DNSKEY.
VAL_A_ALGO_NOT_SUPPORTED: returned if the DNSKEY or DS algorithm
was not supported.
VAL_A_UNKNOWN_ALGO: returned if the DNSKEY or DS algorithm was
unknown.
VAL_A_ALGO_REFUSED: returned if the DNSKEY or DS algorithm was
not allowed as per local policy.
5. Context Management and Validator Policy API
Applications can use local policy to influence the validation
outcome. Examples of local policy elements include trust anchors for
different zones and untrusted algorithms for cryptographic keys and
hashes. Local policy may be different for different applications and
operating scenarios.
Local policy for the validator is stored in the local configration
system (typically the configuration file, /etc/dnsval.conf).
Policies are identified by simple text strings called labels, which
must be unique within the configuration system. As an example,
"browser" could be used as the label that defines the validator
policy for all web-browsers in a system. A label value of ":"
identifies the "default" policy, or the policy that is used when a
NULL context is specified as the ctx parameter for functions in
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Section 4 and Section 3. The default policy is unique within the
configuraion system. Furthermore, the ':' character is only allowed
in the default policy label. The configuration system must flag an
error if some other label contains the ':' character.
Policy definitions have the following structure.
<label> <attribute> <additional-data>;
Currently the only defined value for <attribute> is "trust-anchor".
The value for <additional-data> depends on the type of attribute
specified. For the "trust-anchor" attribute this is a sequence of
the zone name and a quoted string containing the RDATA portion for
the trust anchor's DNSKEY. An example is given below.
browser trust-anchor example.com "257 3 5 AQO8XS4y9r77X9SHBmrx \
MoJf1Pf9AT9Mr/L5BBGtO9/e9f/zl4FFgM2l B6M2XEm6mp6 \
mit4tzpB/sAEQw1McYz6bJdKkTiqtuWTCfDmgQhI6/Ha0 Ef \
GPNSqnY 99FmbSeWNIRaa4fgSCVFhvbrYq1nXkNVyQPeEVHk \
oDNCAlr qOA3lw==" ;
5.1. val_create_context, val_free_context
int val_create_context( const char *scope,
val_context_t **newcontext );
void val_free_context( val_context_t *context );
The val_create_context() creates a handle to a validator policy
context. The scope parameter identifies the particular policy to be
used as the active policy for the context during validation. Policy
scopes have a hierarchical organization, with each member in the
hierarchy separated by the ':' character. The default policy forms
the base of this hierarchy. The validator forms an effective policy
by cumulatively applying the policies for each member in the
hierarchy. For example, for the policy scope "mozilla:browser", the
effective policy is computed by applying policies for the default
":", "browser" and "mozilla" policies, in that order. A NULL scope
creates a context with the default base policy .
The val_create_context() function returns 0 on success, and an error
code from Section 6.1 on failure. The newly created context is
returned in the newcontext field. A NULL context is returned if an
error is encountered. The application must release the memory
allocated after a successful call to the val_create_context()
function using the val_free_context() function.
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5.2. val_get_policy_definition, val_set_policy_definition
int val_get_policy_definition(char *label,
char **pol_def );
int val_set_policy_definition(const char *label,
char *policy_string );
The val_get_policy_definition() function allows applications to
obtain the policy definition for a given label identifier. A NULL
label returns the definition for the default policy. Memory for
pol_def, if the definition for label exists, is internally allocated
and must be released by the application after use.
The val_set_policy_definition() function allows an application to
modify the definition of an existing policy or define a new policy
label within the configuration system. A NULL label updates the
default policy. The rules for a valid label in the above calls are
same as that for labels within the configuration system in that the
':' character is only allowed in the default policy label.
The above functions return 0 on success and an error code from
Section 6.1 on failure.
6. Validation Status Codes and Return Values
The following sections specify the values that may be returned as the
validation status value for the val_status_t parameter type in the
high-level and low-level APIs, and the return values for the low-
level and context-management APIs. The High-level API mirrors
existing legacy DNS-related functions, so the return values from
these functions are identical to their predecessors.
6.1. Return Values
The following values may be returned by functions in the low-level
and context-management APIs.
VAL_NOT_IMPLEMENTED: returned if the implementation did not support
a particular feature.
VAL_BAD_ARGUMENT: returned if an unexpected value was passed as an
argument to a function.
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VAL_INTERNAL_ERROR: returned if an internal error was encountered in
the validator library.
VAL_NO_PERMISSION: returned if the application lacked sufficient
privileges to perform an operation.
VAL_RESOURCE_UNAVAILABLE: returned if some resource necessary for an
operation was unavailable.
VAL_CONF_PARSE_ERROR: returned if the validator configuration was
improperly specified in the configuration system.
VAL_CONF_NOT_FOUND: returned if the validator configuration could
not be located in the configuration system.
VAL_NO_POLICY: returned if the policy identifier being referenced
was invalid.
6.2. Validation Status Codes
Possible values for the validator status codes as returned in the
variable of type val_status_t are listed below.
VAL_LOCAL_ANSWER: returned if the response was obtained locally (for
example, a file such as /etc/hosts).
VAL_BARE_RRSIG: returned if the response was for a query of type
RRSIG. RRSIGs contain the cryptographic signatures for other DNS
data and cannot themselves be validated.
VAL_NONEXISTENT_NAME: returned if the proof for denial of existence
for a domain name was validated successfully.
VAL_NONEXISTENT_TYPE: returned if the proof for denial of existence
for the resource record type for the name queried was validate
successfully.
VAL_ERROR: returned if the an error was encountered while validating
the authentication chain.
VAL_INDETERMINATE: returned if the validator lacked data required to
complete validation down the authentication chain.
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VAL_BOGUS: returned if the response could not be validated due to
signature verification failures or inability to verify proofs.
VAL_PROVABLY_UNSECURE: returned if the record or some ancestor of
the record in the authentication chain towards the trust anchor
was known to be provably unsecure. This condition is treated as
equivalent to a trust point being reached.
VAL_NOTRUST: returned if all available components in the
authentication chain were successfully verified but there was no
trust anchor available.
VAL_SUCCESS: returned if the response was verified and validated.
In cases where a DNS error is returned for the initial query, the
resolver-related error values listed in Section 4.2 are also returned
in val_status_t, offset by the value of VAL_DNS_ERROR_BASE.
7. IANA Considerations
This document has no actions for IANA.
8. Security Considerations
The validator API functions return a status of VAL_LOCAL_ANSWER if
they are returned an answer to a given query from the local
configuration system (for example, from the /etc/hosts file). The
application cannot assume that these answers are trustworthy, unless
the application is certain that local data (such the /etc/hosts file)
is also trustworthy. If this information is modified during a DHCP
lookup, for example, the client system should ensure that the DHCP
server is a trusted source, and that the communication path between
the DHCP server and the client system is secured. If these
conditions are not satisfied and if the application chooses to trust
a validation status of VAL_LOCAL_ANSWER, there exists a potential
attack vector whereby an attacker can poison the configuration system
and an application using this API may trust the result.
Applications will consider data from provably unsecure zones to be
trusted. The same effect is observed if a VAL_FLAGS_DONT_VALIDATE
flag is passed to the val_resolve_and_check() function. Not
performing validation and having a zone that has DNSSEC intentionally
turned off is no worse than the current situation of DNSSEC-unaware
applications not being able to detect the integrity of DNS data.
The DNS search path may affect the result of validation, especially
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in the current Internet environment where not all DNS name servers
are expected to be DNSSEC-aware. If the name server pointed to by
the configuration system is not DNSSEC-aware (i.e. it does not return
DNSSEC records), validation will not be performed. The list of
default name servers (such as in the file /etc/resolv.conf file) is
typically modified by DHCP clients. Hence, if the client system uses
DHCP, it must ensure that the DHCP server is a trusted source, and
that the communication path between the DHCP server and the client
system is secured.
The validator configuration information needs to be protected so that
it cannot be overwritten by unauthorized users or processes. Access
to the val_set_policy_definition() function must similarly be
controlled to prevent malicious changes to the validator policy.
Configuration for the validator also contains the trust anchors for
classes of applications. The system administrator must ensure that
the list of trust anchors are kept up-to-date in the event of key-
rollovers. If the trust anchors are outdated, the validator may not
be able to perform validation or may create the false impression of
having successfully validated a response when it should have been
flagged as bogus.
9. Acknowledgements
We would like to acknowledge the following individuals who have
provided valuable feedback and suggestions for improving this
document: Lindy Foster, Wayne Morrison, Russ Mundy, Bill Sommerfeld,
Robert Story, Wes Hardaker. We would like to acknowledge our other
team members at SPARTA for their inputs and suggestions while
developing the validator API. The list of authentication status
codes listed in Section 4.2 was generated through multiple
brainstorming sessions by the "apps" sub-working group at the IETF
meetings. This draft draws on the results from that effort.
10. References
10.1. Normative References
[1] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493,
February 2003.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
March 2005.
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[3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Resource Records for the DNS Security Extensions", RFC 4034,
March 2005.
[4] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Protocol Modifications for the DNS Security Extensions",
RFC 4035, March 2005.
10.2. Informative References
[5] "DNSSEC-Tools", <http://www.dnssec-tools.org>.
Authors' Addresses
Suresh Krishnaswamy
SPARTA, Inc.
7110 Samuel Morse Dr.
Columbia, MD 21046
US
Email: suresh AT sparta.com
Abhijit Hayatnagarkar
SPARTA, Inc.
7110 Samuel Morse Dr.
Columbia, MD 21046
US
Email: abhijit AT sparta.com
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