-spec cacerts_clear() -> boolean().

Clears any loaded CA certificates, returns true if any was loaded.

-spec cacerts_get() -> [combined_cert()].

Returns the trusted CA certificates if any are loaded, otherwise uses cacerts_load/0 to load them. The function fails if no cacerts could be loaded.

-spec cacerts_load() -> ok | {error, Reason :: term()}.

Loads the OS supplied trusted CA certificates.

This can be overridden by setting the cacerts_path environment key of the public_key application with the location of an alternative certificate. You can set it via the command line as:

erl -public_key cacerts_path '"/path/to/certs.pem"'

Use it with care. It is your responsibility to ensure that the certificates found in this alternative path can be trusted by the running system.

-spec cacerts_load(File :: file:filename_all()) -> ok | {error, Reason :: term()}.

Loads the trusted CA certificates from a file.

-spec pkix_decode_cert(Cert, Type) ->
                          #'Certificate'{tbsCertificate :: term(),
                                         signatureAlgorithm :: term(),
                                         signature :: term()} |
                          #'OTPCertificate'{tbsCertificate :: term(),
                                            signatureAlgorithm :: term(),
                                            signature :: term()}
                          when Cert :: der_encoded(), Type :: plain | otp.

Decodes an ASN.1 DER-encoded PKIX certificate.

Option otp uses the customized ASN.1 specification OTP-PKIX.asn1 for decoding and also recursively decode most of the standard parts.

-spec pkix_encode(Asn1Type, Entity, Type) -> Der
                     when
                         Asn1Type :: asn1_type(),
                         Entity :: term(),
                         Type :: otp | plain,
                         Der :: der_encoded().

DER encodes a PKIX x509 certificate or part of such a certificate.

This function must be used for encoding certificates or parts of certificates that are decoded/created in the otp format, whereas for the plain format this function directly calls der_encode/2.

Note

Subtle ASN-1 encoding errors in certificates may be worked around when decoding, this may have the affect that the encoding a certificate back to DER may generate different bytes then the supplied original.

-spec pkix_hash_type(HashOid :: oid()) -> DigestType :: md5 | crypto:sha1() | crypto:sha2().

Translates OID to Erlang digest type

-spec pkix_is_fixed_dh_cert(Cert) -> boolean() when Cert :: cert().

Checks if a certificate is a fixed Diffie-Hellman certificate.

-spec pkix_is_issuer(CertorCRL, IssuerCert) -> boolean()
                        when
                            CertorCRL ::
                                cert() |
                                #'CertificateList'{tbsCertList :: term(),
                                                   signatureAlgorithm :: term(),
                                                   signature :: term()},
                            IssuerCert :: cert().

Checks if IssuerCert issued Cert.

-spec pkix_is_self_signed(Cert) -> boolean() when Cert :: cert().

Checks if a certificate is self-signed.

-spec pkix_issuer_id(Cert, IssuedBy) -> {ok, ID :: cert_id()} | {error, Reason}
                        when Cert :: cert(), IssuedBy :: self | other, Reason :: term().

Returns the x509 certificate issuer id, if it can be determined.

-spec pkix_normalize_name(Issuer) -> Normalized
                             when Issuer :: issuer_name() | der_encoded(), Normalized :: issuer_name().

Normalizes an issuer name so that it can be easily compared to another issuer name.

-spec pkix_path_validation(Cert, CertChain, Options) ->
                              {ok, {PublicKeyInfo, ConstrainedPolicyNodes}} |
                              {error, {bad_cert, Reason :: bad_cert_reason()}}
                              when
                                  Cert :: cert() | combined_cert() | atom(),
                                  CertChain :: [cert() | combined_cert()],
                                  Options ::
                                      [{max_path_length, integer()} | {verify_fun, {fun(), term()}}],
                                  PublicKeyInfo :: public_key_info(),
                                  ConstrainedPolicyNodes :: [policy_node()].

Performs a basic path validation according to RFC 5280.

However, CRL validation is done separately by pkix_crls_validate/3 and is to be called from the supplied verify_fun. The policy tree check was added in OTP-26.2 and if the certificates include policies the constrained policy set with potential qualifiers will be returned, these values are derived from the policy tree created as part of the path validation algorithm. The constrained set can be constrained only by the Certificate Authorities or also by the user when the option policy_set is provided to this function. The qualifiers convey information about the valid policy and is intended as information to end users.

Available options:

• {verify_fun, {fun(), UserState::term()} - The fun must be defined as:

  fun(OtpCert :: #'OTPCertificate'{},
      Event :: {bad_cert, Reason :: bad_cert_reason() | {revoked, atom()}} |
               {extension, #'Extension'{}},
      UserState :: term()) ->
    {valid, UserState :: term()} |
    {valid_peer, UserState :: term()} |
    {fail, Reason :: term()} |
    {unknown, UserState :: term()}.

  or as:

  fun(OtpCert :: #'OTPCertificate'{},
      DerCert :: der_encoded(),
      Event :: {bad_cert, Reason :: bad_cert_reason() | {revoked, atom()}} |
               {extension, #'Extension'{}},
      UserState :: term()) ->
    {valid, UserState :: term()} |
    {valid_peer, UserState :: term()} |
    {fail, Reason :: term()} |
    {unknown, UserState :: term()}.

  The verify callback can have 3 or 4 arguments in case the DER encoded version is needed by the callback.

  If the verify callback fun returns {fail, Reason}, the verification process is immediately stopped. If the verify callback fun returns {valid, UserState}, the verification process is continued. This can be used to accept specific path validation errors, such as selfsigned_peer, as well as verifying application-specific extensions. If called with an extension unknown to the user application, the return value {unknown, UserState} is to be used.

  Note

  If you need the DER encoded version of the certificate and have the OTP decoded version encoding it back can fail to give the correct result, due to work arounds for common misbehaving encoders. So it is recommended to call pkix_path_validation with Cert and CertChain arguments as der_encoded() | #cert{} and [der_encoded() | #cert{}]. Also note that the path validation itself needs both the encoded and the decoded version of the certificate.

  Warning

  Note that user defined custom verify_fun may alter original path validation error (e.g selfsigned_peer). Use with caution.

• {max_path_length, integer()} - The max_path_length is the maximum number of non-self-issued intermediate certificates that can follow the peer certificate in a valid certification path. So, if max_path_length is 0, the PEER must be signed by the trusted ROOT-CA directly, if it is 1, the path can be PEER, CA, ROOT-CA, if it is 2, the path can be PEER, CA, CA, ROOT-CA, and so on.

• {policy_set, [oid()]}(Since OTP 26.2)
  The set of policies that will be accepted, defaults to the special value [?anyPolicy] that will accept all policies.

• {explicit_policy, boolean()}(Since OTP 26.2)
  Explicitly require that each certificate in the path must include at least one of the certificate policies in the policy_set.

• {inhibit_policy_mapping, boolean()}(Since OTP 26.2)
  Prevent policies to be mapped to other policies.

• {inhibit_any_policy, boolean()}(Since OTP 26.2)
  Prevent the special policy ?anyPolicy from being accepted.

Explanations of reasons for a bad certificate:

• cert_expired - Certificate is no longer valid as its expiration date has passed.

• invalid_issuer - Certificate issuer name does not match the name of the issuer certificate in the chain.

• invalid_signature - Certificate was not signed by its issuer certificate in the chain.

• name_not_permitted - Invalid Subject Alternative Name extension.

• missing_basic_constraint - Certificate, required to have the basic constraints extension, does not have a basic constraints extension.

• invalid_key_usage - Certificate key is used in an invalid way according to the key-usage extension.

• {revoked, crl_reason()} - Certificate has been revoked.

• invalid_validity_dates - The validity section of the X.509 certificate(s) contains invalid date formats not matching the RFC.

• atom() - Application-specific error reason that is to be checked by the verify_fun.

-spec pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}
                         when
                             AlgorithmId :: oid(),
                             DigestType :: digest_type(),
                             SignatureType :: rsa | dsa | ecdsa | eddsa.

Translates signature algorithm OID to Erlang digest and signature types.

The AlgorithmId is the signature OID from a certificate or a certificate revocation list.

-spec pkix_subject_id(Cert) -> ID when Cert :: cert(), ID :: cert_id().

Returns the X509 certificate subject id.

-spec pkix_verify_hostname(Cert, ReferenceIDs) -> boolean()
                              when
                                  Cert :: cert(),
                                  ReferenceIDs ::
                                      [{uri_id | dns_id | ip | srv_id | atom() | oid(), string()} |
                                       {ip, inet:ip_address() | string()}].

Equivalent to pkix_verify_hostname(Cert, ReferenceIDs, []).

-spec pkix_verify_hostname(Cert, ReferenceIDs, Options) -> boolean()
                              when
                                  Cert :: cert(),
                                  ReferenceIDs ::
                                      [{uri_id | dns_id | ip | srv_id | atom() | oid(), string()} |
                                       {ip, inet:ip_address() | string()}],
                                  Options :: [{match_fun | fail_callback | fqdn_fun, fun()}].

This function checks that the Presented Identifier (e.g hostname) in a peer certificate is in agreement with at least one of the Reference Identifier that the client expects to be connected to.

The function is intended to be added as an extra client check of the peer certificate when performing public_key:pkix_path_validation/3

See RFC 6125 for detailed information about hostname verification. The User's Guide and code examples describes this function more detailed.

The option funs are described here:

• match_fun

  fun(ReferenceId::ReferenceId() | FQDN::string(),
      PresentedId::{dNSName,string()} | {uniformResourceIdentifier,string() |
                   {iPAddress,list(byte())} | {OtherId::atom()|oid(),term()}})

  This function replaces the default host name matching rules. The fun should return a boolean to tell if the Reference ID and Presented ID matches or not. The match fun can also return a third value, value, the atom default, if the default matching rules shall apply. This makes it possible to augment the tests with a special case:

  fun(....) -> true;   % My special case
     (_, _) -> default % all others falls back to the inherit tests
  end

  See pkix_verify_hostname_match_fun/1 for a function that takes a protocol name as argument and returns a fun/2 suitable for this option and Re-defining the match operation in the User's Guide for an example.

  Note

  Reference Id values given as binaries will be converted to strings, and ip references may be given in string format that is "10.0.1.1" or "1234::5678:9012" as well as on the format inet:ip_address/0

• fail_callback - If a matching fails, there could be circumstances when the certificate should be accepted anyway. Think for example of a web browser where you choose to accept an outdated certificate. This option enables implementation of such an exception but for hostnames. This fun/1 is called when no ReferenceID matches. The return value of the fun (a boolean/0) decides the outcome. If true the the certificate is accepted otherwise it is rejected. See "Pinning" a Certificate in the User's Guide.

• fqdn_fun - This option augments the host name extraction from URIs and other Reference IDs. It could for example be a very special URI that is not standardised. The fun takes a Reference ID as argument and returns one of:

  • the hostname
  • the atom default: the default host name extract function will be used
  • the atom undefined: a host name could not be extracted. The pkix_verify_hostname/3 will return false.

  For an example, see Hostname extraction in the User's Guide.

-spec pkix_verify_hostname_match_fun(Protocol) -> Result when Protocol :: https, Result :: fun().

The return value of calling this function is intended to be used in the match_fun option in pkix_verify_hostname/3.

The returned fun augments the verify hostname matching according to the specific rules for the protocol in the argument.

Note

Currently supported https fun will allow wildcard certificate matching as specified by the HTTP standard. Note that for instance LDAP have a different set of wildcard matching rules. If you do not want to allow wildcard certificates (recommended from a security perspective) or otherwise customize the hostname match the default match function used by ssl application will be sufficient.