DNS Extensions S. Krishnaswamy Internet-Draft A. Hayatnagarkar Expires: December 26, 2006 SPARTA, Inc. June 24, 2006 DNSSEC Validator API draft-hayatnagarkar-dnsext-validator-api-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 26, 2006. 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. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 1] Internet-Draft DNSSEC Validator API June 2006 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 . . . . . . . . . . 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_switch_policy_scope . . . . . . . . . . . . . . . . . 18 5.3. val_get_scopes_within_context . . . . . . . . . . . . . . 18 5.4. val_get_scope_definition, val_set_scope_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 . . . . . . . . . . . . . . . . . . . . . . . . 24 Intellectual Property and Copyright Statements . . . . . . . . . . 25 Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 2] Internet-Draft DNSSEC Validator API June 2006 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 returned records. This document presents an API between an application and a validator. The API functions provide a convenient way for applications to control the DNSSEC validation process, and to obtain and use results of the validation process to control their 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(), or for applications that have no requirement for detailed validation status information. The low-level validator API gives more control over the validation process and allows detailed inspection of validation status for each element of the authentication chain [2]. Results returned by the validator can be guided by local policy decisions. 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 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 terminology used in this specification are defined below: Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 3] Internet-Draft DNSSEC Validator API June 2006 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. base policy: the default policy definition that is associated with a validator context. The base policy can be different for different validator contexts. policy scope: a customization within the base policy to address the requirements of a particular operating scenario. Policy scopes are useful when it becomes necessary to override certain policy attributes in specific environments. As an example, an application may require different validator policies for a web browser and a mail client. In such cases the application may define a common base policy for the system and have overrides for specific scopes: one for the web browser and one for the mail client. 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 of type val_context_t* 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. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 4] Internet-Draft DNSSEC Validator API June 2006 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() and val_gethostbyname_r() functions perform name-to-address translation while the val_gethostbyaddr() and val_gethostbyaddr_r() functions perform the address-to-name translation. These functions are DNSSEC-aware versions of the gethostbyname(), gethostbyname_r(), gethostbyaddr() and gethostbyaddr_r() functions and can be used by applications to get the validation status of DNS queries performed during the name-to- address or address-to-name translations. The parameters to the above functions closely mirror the legacy functions and must be only used when replacing such functions with their DNSSEC-aware counterparts. For applications that do not already use these older functions it is instead recommended to use 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 Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 5] Internet-Draft DNSSEC Validator API June 2006 type hostent for the host name provided in the name parameter. 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 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 value may point to static data, and it may be overwritten by subsequent calls. Copying the struct hostent does not suffice since it 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, which has the type val_status_t, contains the status of DNSSEC validation. Possible values for val_status_t 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, have been validated successfully. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 6] Internet-Draft DNSSEC Validator API June 2006 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() 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. 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 Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 7] Internet-Draft DNSSEC Validator API June 2006 translation in a protocol independent manner. It is a DNSSEC-aware version of the getnameinfo() function (RFC 3493 [1]). In addition to the values returned by the getnameinfo() function, it returns the DNSSEC validation status via the val_status parameter. The syntax and semantics of other parameters in val_getnameinfo() are identical to that specified in [1]. val_status will contain a validation status of VAL_SUCCESS only if both the address and canonical name within the val_addrinfo structure, if present, have been validated successfully. The validation status value can be displayed in a human-understandable 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 give the status of DNSSEC validation. They are intended as DNSSEC-aware replacements for the res_query() function. 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 is for a type of ANY or when a proof of non-existence is returned, in which case, RRsets of type Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 8] Internet-Draft DNSSEC Validator API June 2006 NSEC and SOA may also be returned. The val_query() function returns 0 on success and a non-zero error code on failure. When a success value is returned, the memory pointed to by resp contains a linked-list of responses returned by the validator. 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. 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 human-understandable 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. At present only one flag is defined: VAL_QUERY_MERGE_RRSETS. 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 have been successfully validated. 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 proper set of arguments and returning 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 human-understandable format. The returned values are essentially string representations of the definitions given in Section 6.2. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 9] Internet-Draft DNSSEC Validator API June 2006 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 Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 10] Internet-Draft DNSSEC Validator API June 2006 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( struct val_result_chain *results ); struct val_result_chain { val_status_t val_rc_status; struct val_authentication_chain *val_rc_trust; 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; struct val_authentication_chain *val_ac_rrset_next; }; struct val_rrset { u_int8_t *val_msg_header; u_int16_t val_msg_headerlen; u_int8_t *val_queryset_data; u_int16_t val_queryset_datalen; 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 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; }; char *p_as_error(val_astatus_t err); The val_resolve_and_check() function queries a set of name servers for the tuple and then verifies and validates the responses received. The verification step checks Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 11] Internet-Draft DNSSEC Validator API June 2006 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. The flags field is currently unused. 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() 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. Multiple RRs within the RRset are all part of the same answer. Multiple answers are possible when the query type is ANY or when a proof of non-existence is returned, in which case RRsets of type NSEC and SOA may also be returned. The val_rc_next field can be 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 human-understandable 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 chain. The val_rc_trust field in the val_result_chain structure points to the first element in the inverted authentication chain sequence. 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 human-understandable format using the p_as_error() function. The val_ac_rrset_next field points to the next RRset within the set of responses returned for a query. The val_ac_trust field points to the next element in the inverted authentication chain. For a element with type DNSKEY, this would correspond to a DS record in the parent zone and for a DS record this would correspond 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 case of an error when the next node in the authentication chain cannot be constructed. The val_ac_status field Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 12] Internet-Draft DNSSEC Validator API June 2006 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), the query section of the DNS response in which the RRset was received (in the val_queryset_data field with length given by the val_queryset_datalen 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 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 essentially a list of name-value pairs corresponding to each resource-record within the RRset. Members of the val_rrset_sig linked list also have an rr_status field which indicates whether the signature verified succesfully over the corresponding RRset or not. Although rr_status is of type val_astatus_t, this field only takes on a subset of status values defined in Section 4.2), specifically those pertaining to signature verification. 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_ANS: returned if the RRset was present in the answer section of the DNS response. VAL_FROM_AUT: returned if the RRset was present in the authority section of the DNS response. VAL_FROM_ADD: returned if the RRset was present in the additional section of the DNS response. 4.2. Assertion Status Codes The verification status value stored in the val_ac_status member of the val_authentication_chain structure can have one of the following values: Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 13] Internet-Draft DNSSEC Validator API June 2006 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_NO_TRUST_ANCHOR: returned if there was no trust anchor configured for a given authentication chain. VAL_A_UNTRUSTED_ZONE: returned if local policy defines a given zone to be untrusted. VAL_A_IRRELEVANT_PROOF: returned if the proof of nonexistence returned for a query is ambiguous. VAL_A_DNSSEC_VERSION_ERROR: returned if the DNSSEC version is unrecognized. VAL_A_TOO_MANY_LINKS: returned if local policy identifies a given authentication chain to be too long. VAL_A_UNKNOWN_DNSKEY_PROTO: returned if the DNSKEY protocol number is unrecognized. VAL_A_DNSKEY_NOMATCH: returned if an RRSIG was created by a DNSKEY that does not exist in the apex keyset. VAL_A_WRONG_LABEL_COUNT: returned if the number of labels on the signature is greater than the the count given in the RRSIG RDATA. VAL_A_SECURITY_LAME: returned if an was RRSIG created with a key that does not exist in the parent DS record set. VAL_A_NOT_A_ZONE_KEY: returned if the key used to verify the RRSIG is not valid DNSKEY. VAL_A_RRSIG_NOTYETACTIVE: returned if the RRSIG's inception time is in the future. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 14] Internet-Draft DNSSEC Validator API June 2006 VAL_A_RRSIG_EXPIRED: returned if the RRSIG has expired. VAL_A_ALGO_NOT_SUPPORTED: returned if the algorithm in the DNSKEY, RRSIG or DS resource record is not supported. VAL_A_UNKNOWN_ALGO: returned if the DNSKEY, RRSIG or DS algorithm is unknown. VAL_A_RRSIG_VERIFIED: returned if the RRSIG verified successfully. VAL_A_RRSIG_VERIFY_FAILED: returned if the RRSIG did not verify. VAL_A_NOT_VERIFIED: returned if different RRSIGs covering the same resource record failed for different reasons. VAL_A_KEY_TOO_LARGE: returned if local policy has identified the key size as being too large. VAL_A_KEY_TOO_SMALL: returned if local policy has identified the key size as being too small. VAL_A_KEY_NOT_AUTHORIZED: returned if local policy has identified the key to be unauthorized for validation. VAL_A_ALGO_REFUSED: returned if the algorithm in the DNSKEY, RRSIG or DS is not allowed as per local policy. VAL_A_CLOCK_SKEW: returned if the signature over the resource record could only be verified after clock skew is taken into account VAL_A_DUPLICATE_KEYTAG: returned if two different DNSKEYs in a zone have the same keytag. VAL_A_NO_PREFERRED_SEP: returned if there is no DNSKEY in the parent DS set that local policy permits the validator to build its authentication chain from. VAL_A_WRONG_RRSIG_OWNER: returned if the RRSIG and the data that it purportedly covers have differing notions of owner name VAL_A_RRSIG_ALGO_MISMATCH: returned if the DNSKEY and RRSIG pair have a mismatch in their algorithm. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 15] Internet-Draft DNSSEC Validator API June 2006 VAL_A_KEYTAG_MISMATCH: returned if the DNSKEY and RRSIG pair have a mismatch in their key tags 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 has been locally defined to be a trust anchor. VAL_A_TRUST_ZONE: returned if local policy defines a given zone to be trusted. 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. 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_TSIG_ERROR: returned if there was an error in TSIG processing. SR_NO_ANSWER: returned if no answer was received for a query. SR_INTERNAL_ERROR: returned if an internal error was encountered in the resolver. SR_WRONG_ANSWER: returned if a message received was not a valid response to a query. SR_HEADER_BADSIZE: returned if the message size was not consistent with header values. SR_DNS_GENERIC_ERROR: returned if the response was received with the rcode set to one of the well-known error values such as NXDOMAIN, FORMERR, etc. SR_EDNS_VERSION_ERROR: returned if the EDNS0 version was not recognized. Krishnaswamy & Hayatnagarkar Expires December 26, 2006 [Page 16] Internet-Draft DNSSEC Validator API June 2006 SR_UNSUPP_EDNS0_LABEL: returned if the EDNS0 label is not supported. SR_SUSPICIOUS_BIT: returned if some bit in the response headers is unexpectedly set or unset. SR_NAME_EXPANSION_FAILURE: returned if DNS name uncompression failed. SR_MISSING_GLUE: returned if glue records are not available for a referral. SR_CONFLICTING_ANSWERS: returned if multiple answers are returned for a query, and they are inconsistent with each other. 5. Context Management and Validator Policy API Applications can use local policy to influence the decision about when the validator must break out from the process of constructing the authentication chain with either a success or failure condition. 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 labels or simple text strings, which must be unique within the configuration system. As an example, "browser" could be used as the label for a policy that defines the base policy for all web-browsers in a system. A label value of ":" identifies the "default" base policy, or the policy that is used when a NULL context is specified as the ctx parameter for functions in Section 4 and Section 3. Policy definitions have the following structure.