DANE API (GnuTLS 3.8.4)

E.11 DANE API

The following functions are to be used for DANE certificate verification. Their prototypes lie in gnutls/dane.h. Note that you need to link with the libgnutls-dane library to use them.

dane_cert_type_name

Function: const char * dane_cert_type_name (dane_cert_type_t type)

type: is a DANE match type

Convert a dane_cert_type_t value to a string.

Returns: a string that contains the name of the specified type, or NULL .

dane_cert_usage_name

Function: const char * dane_cert_usage_name (dane_cert_usage_t usage)

usage: is a DANE certificate usage

Convert a dane_cert_usage_t value to a string.

Returns: a string that contains the name of the specified type, or NULL .

dane_match_type_name

Function: const char * dane_match_type_name (dane_match_type_t type)

type: is a DANE match type

Convert a dane_match_type_t value to a string.

Returns: a string that contains the name of the specified type, or NULL .

dane_query_data

Function: int dane_query_data (dane_query_t q, unsigned int idx, unsigned int * usage, unsigned int * type, unsigned int * match, gnutls_datum_t * data)

q: The query result structure

idx: The index of the query response.

usage: The certificate usage (see dane_cert_usage_t )

type: The certificate type (see dane_cert_type_t )

match: The DANE matching type (see dane_match_type_t )

data: The DANE data.

This function will provide the DANE data from the query response.

Returns: On success, DANE_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_query_deinit

Function: void dane_query_deinit (dane_query_t q)

q: The structure to be deinitialized

This function will deinitialize a DANE query result structure.

dane_query_entries

Function: unsigned int dane_query_entries (dane_query_t q)

q: The query result structure

This function will return the number of entries in a query.

Returns: The number of entries.

dane_query_status

Function: dane_query_status_t dane_query_status (dane_query_t q)

q: The query result structure

This function will return the status of the query response. See dane_query_status_t for the possible types.

Returns: The status type.

dane_query_tlsa

Function: int dane_query_tlsa (dane_state_t s, dane_query_t * r, const char * host, const char * proto, unsigned int port)

s: The DANE state structure

r: A structure to place the result

host: The host name to resolve.

proto: The protocol type (tcp, udp, etc.)

port: The service port number (eg. 443).

This function will query the DNS server for the TLSA (DANE) data for the given host.

Returns: On success, DANE_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_query_to_raw_tlsa

Function: int dane_query_to_raw_tlsa (dane_query_t q, unsigned int * data_entries, char *** dane_data, int ** dane_data_len, int * secure, int * bogus)

q: The query result structure

data_entries: Pointer set to the number of entries in the query

dane_data: Pointer to contain an array of DNS rdata items, terminated with a NULL pointer; caller must guarantee that the referenced data remains valid until dane_query_deinit() is called.

dane_data_len: Pointer to contain the length n bytes of the dane_data items

secure: Pointer set true if the result is validated securely, false if validation failed or the domain queried has no security info

bogus: Pointer set true if the result was not secure due to a security failure

This function will provide the DANE data from the query response.

The pointers dane_data and dane_data_len are allocated with gnutls_malloc() to contain the data from the query result structure (individual dane_data items simply point to the original data and are not allocated separately). The returned dane_data are only valid during the lifetime of q .

Returns: On success, DANE_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_raw_tlsa

Function: int dane_raw_tlsa (dane_state_t s, dane_query_t * r, char *const * dane_data, const int * dane_data_len, int secure, int bogus)

s: The DANE state structure

r: A structure to place the result

dane_data: array of DNS rdata items, terminated with a NULL pointer; caller must guarantee that the referenced data remains valid until dane_query_deinit() is called.

dane_data_len: the length n bytes of the dane_data items

secure: true if the result is validated securely, false if validation failed or the domain queried has no security info

bogus: if the result was not secure (secure = 0) due to a security failure, and the result is due to a security failure, bogus is true.

This function will fill in the TLSA (DANE) structure from the given raw DNS record data. The dane_data must be valid during the lifetime of the query.

Returns: On success, DANE_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_state_deinit

Function: void dane_state_deinit (dane_state_t s)

s: The structure to be deinitialized

This function will deinitialize a DANE query structure.

dane_state_init

Function: int dane_state_init (dane_state_t * s, unsigned int flags)

s: The structure to be initialized

flags: flags from the dane_state_flags enumeration

This function will initialize the backend resolver. It is intended to be used in scenarios where multiple resolvings occur, to optimize against multiple re-initializations.

Returns: On success, DANE_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_state_set_dlv_file

Function: int dane_state_set_dlv_file (dane_state_t s, const char * file)

s: The structure to be deinitialized

file: The file holding the DLV keys.

This function will set a file with trusted keys for DLV (DNSSEC Lookaside Validation).

dane_strerror

Function: const char * dane_strerror (int error)

error: is a DANE error code, a negative error code

This function is similar to strerror. The difference is that it accepts an error number returned by a gnutls function; In case of an unknown error a descriptive string is sent instead of NULL .

Error codes are always a negative error code.

Returns: A string explaining the DANE error message.

dane_verification_status_print

Function: int dane_verification_status_print (unsigned int status, gnutls_datum_t * out, unsigned int flags)

status: The status flags to be printed

out: Newly allocated datum with (0) terminated string.

flags: should be zero

This function will pretty print the status of a verification process – eg. the one obtained by dane_verify_crt() .

The output out needs to be deallocated using gnutls_free() .

Returns: On success, GNUTLS_E_SUCCESS (0) is returned, otherwise a negative error value.

dane_verify_crt

Function: int dane_verify_crt (dane_state_t s, const gnutls_datum_t * chain, unsigned chain_size, gnutls_certificate_type_t chain_type, const char * hostname, const char * proto, unsigned int port, unsigned int sflags, unsigned int vflags, unsigned int * verify)

s: A DANE state structure (may be NULL)

chain: A certificate chain

chain_size: The size of the chain

chain_type: The type of the certificate chain

hostname: The hostname associated with the chain

proto: The protocol of the service connecting (e.g. tcp)

port: The port of the service connecting (e.g. 443)

sflags: Flags for the initialization of s (if NULL)

vflags: Verification flags; an OR’ed list of dane_verify_flags_t .

verify: An OR’ed list of dane_verify_status_t .

This function will verify the given certificate chain against the CA constrains and/or the certificate available via DANE. If no information via DANE can be obtained the flag DANE_VERIFY_NO_DANE_INFO is set. If a DNSSEC signature is not available for the DANE record then the verify flag DANE_VERIFY_NO_DNSSEC_DATA is set.

Due to the many possible options of DANE, there is no single threat model countered. When notifying the user about DANE verification results it may be better to mention: DANE verification did not reject the certificate, rather than mentioning a successful DANE verification.

Note that this function is designed to be run in addition to PKIX - certificate chain - verification. To be run independently the DANE_VFLAG_ONLY_CHECK_EE_USAGE flag should be specified; then the function will check whether the key of the peer matches the key advertised in the DANE entry.

Returns: a negative error code on error and DANE_E_SUCCESS (0) when the DANE entries were successfully parsed, irrespective of whether they were verified (see verify for that information). If no usable entries were encountered DANE_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.

dane_verify_crt_raw

Function: int dane_verify_crt_raw (dane_state_t s, const gnutls_datum_t * chain, unsigned chain_size, gnutls_certificate_type_t chain_type, dane_query_t r, unsigned int sflags, unsigned int vflags, unsigned int * verify)

s: A DANE state structure (may be NULL)

chain: A certificate chain

chain_size: The size of the chain

chain_type: The type of the certificate chain

r: DANE data to check against

sflags: Flags for the initialization of s (if NULL)

vflags: Verification flags; an OR’ed list of dane_verify_flags_t .

verify: An OR’ed list of dane_verify_status_t .

This is the low-level function of dane_verify_crt() . See the high level function for documentation.

This function does not perform any resolving, it utilizes cached entries from r .

dane_verify_session_crt

Function: int dane_verify_session_crt (dane_state_t s, gnutls_session_t session, const char * hostname, const char * proto, unsigned int port, unsigned int sflags, unsigned int vflags, unsigned int * verify)

s: A DANE state structure (may be NULL)

session: A gnutls session

hostname: The hostname associated with the chain

proto: The protocol of the service connecting (e.g. tcp)

port: The port of the service connecting (e.g. 443)

sflags: Flags for the initialization of s (if NULL)

vflags: Verification flags; an OR’ed list of dane_verify_flags_t .

verify: An OR’ed list of dane_verify_status_t .

This function will verify session’s certificate chain against the CA constrains and/or the certificate available via DANE. See dane_verify_crt() for more information.

This will not verify the chain for validity; unless the DANE verification is restricted to end certificates, this must be be performed separately using gnutls_certificate_verify_peers3() .