API module for public-key infrastructure.

Provides functions to handle public-key infrastructure, for details see public_key(6).


All records used in this Reference Manual are generated from ASN.1 specifications and are documented in the User's Guide. See Public-key Records.

Use the following include directive to get access to the records and constant macros described here and in the User's Guide:


Object identifier, a tuple of integers as generated by the ASN.1 compiler.

Macro names for key object identifiers used by prefixing with ?

ASN.1 type present in the Public Key applications ASN.1 specifications.

Macro names for object identifiers for EDDSA curves used by prefixing with ?


OthersECDHkey = #'ECPoint'{}
MyECDHkey = #'ECPrivateKey'{}
SharedSecret = binary()

Computes shared secret.


Asn1Type = asn1_type()
Entity = term()

Decodes a public-key ASN.1 DER encoded entity.


Asn1Type = asn1_type()
Entity = term()
Der = binary()

Encodes a public-key entity with ASN.1 DER encoding.


MinSize = SuggestedSize = MaxSize = integer() >= 1
Groups = undefined | [{Size, [Group]}]
Group = {G, P}

Selects a group for Diffie-Hellman key exchange with the key size in the range MinSize...MaxSize and as close to SuggestedSize as possible. If Groups == undefined a default set will be used, otherwise the group is selected from Groups.

First a size, as close as possible to SuggestedSize, is selected. Then one group with that key size is randomly selected from the specified set of groups. If no size within the limits of MinSize and MaxSize is available, {error,no_group_found} is returned.

The default set of groups is listed in lib/public_key/priv/moduli. This file may be regenerated like this:

	$> cd $ERL_TOP/lib/public_key/priv/
	$> generate
         ---- wait until all background jobs has finished. It may take several days !
	$> cat moduli-* > moduli
	$> cd ..; make 


DHparams = #'DHParameter'{}
DHkeys = {PublicDH :: binary(), PrivateDH :: binary()}
ECkey = #'ECPrivateKey'{}
RSAparams = {rsa, Size, PubExp}
Size = PubExp = integer() >= 1
RSAkey = #'RSAPrivateKey'{}

Generates a new key pair. Note that except for Diffie-Hellman the public key is included in the private key structure. See also crypto:generate_key/2

Decodes PEM binary data and returns entries as ASN.1 DER encoded entities.

Example {ok, PemBin} = file:read_file("cert.pem"). PemEntries = public_key:pem_decode(PemBin).

pem_entry_decode(PemEntry) -> term()

pem_entry_decode(PemEntry, Password) -> term()


PemEntry = pem_entry()
Password = string() | fun(() -> string())

Decodes a PEM entry. pem_decode/1 returns a list of PEM entries. Notice that if the PEM entry is of type 'SubjectPublickeyInfo', it is further decoded to an rsa_public_key() or dsa_public_key().

Password can be either an octet string or function which returns same type.

pem_entry_encode(Asn1Type, Entity) -> pem_entry()

pem_entry_encode(Asn1Type, Entity, InfoPwd) -> pem_entry()


Asn1Type = pki_asn1_type()
Entity = term()
InfoPwd = {CipherInfo, Password}
CipherInfo = cipher_info()
Password = string()

Creates a PEM entry that can be feed to pem_encode/1.

If Asn1Type is 'SubjectPublicKeyInfo', Entity must be either an rsa_public_key(), dsa_public_key() or an ec_public_key() and this function creates the appropriate 'SubjectPublicKeyInfo' entry.


Cert = der_cert()
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.


Asn1Type = asn1_type()
Entity = term()
Type = otp | plain

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.


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.


CertorCRL = cert() | #'CertificateList'{}
IssuerCert = cert()

Checks if IssuerCert issued Cert.


Cert = cert()

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


Cert = cert()

Checks if a certificate is self-signed.


Cert = cert()
IssuedBy = self | other
Reason = term()

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


Normalized = issuer_name()

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


Cert = cert() | atom()
CertChain = [cert() | combined_cert()]
Options =
    [{max_path_length, integer()} |
     {verify_fun, {function(), term()}}]
PublicKeyInfo = public_key_info()
PolicyTree = list()

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 optional policy tree check is currently not implemented but an empty place holder list is returned instead.

Available options:

{verify_fun, {fun(), InitialUserState::term()}

The fun must be defined as:

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

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 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.

Explanations of reasons for a bad certificate:


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


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


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


Invalid Subject Alternative Name extension.


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


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

{revoked, crl_reason()}

Certificate has been revoked.


Application-specific error reason that is to be checked by the verify_fun.


CRL = der_encoded() | #'CertificateList'{}
Issuer = issuer_name()

Returns the issuer of the CRL.


OTPcertificate = #'OTPCertificate'{}
DPandCRLs = [DPandCRL]
DPandCRL = {DP, {DerCRL, CRL}}
DP = #'DistributionPoint'{}
DerCRL = der_encoded()
CRL = #'CertificateList'{}
Options = [{atom(), term()}]
CRLstatus = valid | {bad_cert, BadCertReason}
BadCertReason =
    revocation_status_undetermined |
    {revocation_status_undetermined, Reason :: term()} |
    {revoked, crl_reason()}

Performs CRL validation. It is intended to be called from the verify fun of pkix_path_validation/3 .

Available options:

{update_crl, fun()}

The fun has the following type specification:

 fun(#'DistributionPoint'{}, #'CertificateList'{}) ->

The fun uses the information in the distribution point to access the latest possible version of the CRL. If this fun is not specified, Public Key uses the default implementation:

 fun(_DP, CRL) -> CRL end
{issuer_fun, fun()}

The fun has the following type specification:

fun(#'DistributionPoint'{}, #'CertificateList'{},
    {rdnSequence,[#'AttributeTypeAndValue'{}]}, term()) ->
	{ok, #'OTPCertificate'{}, [der_encoded]}

The fun returns the root certificate and certificate chain that has signed the CRL.

 fun(DP, CRL, Issuer, UserState) -> {ok, RootCert, CertChain}
{undetermined_details, boolean()}

Defaults to false. When revocation status cannot be determined, and this option is set to true, details of why no CRLs where accepted are included in the return value.


CRL = der_encoded() | #'CertificateList'{}
Cert = cert()

Verify that Cert is the CRL signer.


Cert = cert()
DistPoint = #'DistributionPoint'{}

Creates a distribution point for CRLs issued by the same issuer as Cert. Can be used as input to pkix_crls_validate/3


Cert = cert()
DistPoints = [#'DistributionPoint'{}]

Extracts distribution points from the certificates extensions.

Translates OID to Erlang digest type


CRL = der_encoded() | #'CertificateList'{}
DistPoint = #'DistributionPoint'{}

Checks whether the given distribution point matches the Issuing Distribution Point of the CRL, as described in RFC 5280. If the CRL doesn't have an Issuing Distribution Point extension, the distribution point always matches.


Cert = #'OTPTBSCertificate'{}

Signs an 'OTPTBSCertificate'. Returns the corresponding DER-encoded certificate.


AlgorithmId = oid()
DigestType = crypto:rsa_digest_type() | none
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.


ChainConf =
    #{server_chain := chain_opts(), client_chain := chain_opts()} |
TestConf = test_config() | [conf_opt()]

Creates certificate configuration(s) consisting of certificate and its private key plus CA certificate bundle, for a client and a server, intended to facilitate automated testing of applications using X509-certificates, often through SSL/TLS. The test data can be used when you have control over both the client and the server in a test scenario.

When this function is called with a map containing client and server chain specifications; it generates both a client and a server certificate chain where the cacerts returned for the server contains the root cert the server should trust and the intermediate certificates the server should present to connecting clients. The root cert the server should trust is the one used as root of the client certificate chain. Vice versa applies to the cacerts returned for the client. The root cert(s) can either be pre-generated with pkix_test_root_cert/2 , or if options are specified; it is (they are) generated.

When this function is called with a list of certificate options; it generates a configuration with just one node certificate where cacerts contains the root cert and the intermediate certs that should be presented to a peer. In this case the same root cert must be used for all peers. This is useful in for example an Erlang distributed cluster where any node, towards another node, acts either as a server or as a client depending on who connects to whom. The generated certificate contains a subject altname, which is not needed in a client certificate, but makes the certificate useful for both roles.

Explanation of the options used to customize certificates in the generated chains:

{digest, digest_type()}

Hash algorithm to be used for signing the certificate together with the key option. Defaults to sha that is sha1.

{key, key_params() | private_key()}

Parameters to be used to call public_key:generate_key/1, to generate a key, or an existing key. Defaults to generating an ECDSA key. Note this could fail if Erlang/OTP is compiled with a very old cryptolib.

{validity, {From::erlang:timestamp(), To::erlang:timestamp()}}

The validity period of the certificate.

{extensions, [#'Extension'{}]}

Extensions to include in the certificate.

Default extensions included in CA certificates if not otherwise specified are:

[#'Extension'{extnID = ?'id-ce-keyUsage',
              extnValue = [keyCertSign, cRLSign],
              critical = false},
#'Extension'{extnID = ?'id-ce-basicConstraints',
             extnValue = #'BasicConstraints'{cA = true},
             critical = true}]

Default extensions included in the server peer cert if not otherwise specified are:

[#'Extension'{extnID = ?'id-ce-keyUsage',
              extnValue = [digitalSignature, keyAgreement],
              critical = false},
#'Extension'{extnID = ?'id-ce-subjectAltName',
             extnValue = [{dNSName, Hostname}],
             critical = false}]

Hostname is the result of calling net_adm:localhost() in the Erlang node where this funcion is called.


Note that the generated certificates and keys does not provide a formally correct PKIX-trust-chain and they cannot be used to achieve real security. This function is provided for testing purposes only.


Name = string()
Options = [cert_opt()]
RootCert = test_root_cert()

Generates a root certificate that can be used in multiple calls to pkix_test_data/1 when you want the same root certificate for several generated certificates.


Cert = cert()

Returns the X509 certificate subject id.


Cert = cert()
ReferenceIDs = referenceIDs()
Options = [{match_fun | fail_callback | fqdn_fun, function()}]

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:

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

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.

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

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()) decides the outcome. If true the the certificate is accepted otherwise it is rejected. See "Pinning" a Certificate in the User's Guide.
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.


Protocol = https
Result = function()

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.


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.


SshBin = binary()
Type = ssh2_pubkey | OtherType | InternalType
OtherType = public_key | ssh_file()
InternalType = new_openssh
Decoded = Decoded_ssh2_pubkey | Decoded_OtherType
Decoded_ssh2_pubkey = public_key() | ed_legacy_pubkey()
Decoded_OtherType =
    [{public_key() | ed_legacy_pubkey(), Attributes}]
Attributes = [{atom(), term()}]

This function is deprecated and should not be used in new programs. Use ssh_file:decode/2 instead.

Decodes an SSH file-binary. In the case of known_hosts or auth_keys, the binary can include one or more lines of the file. Returns a list of public keys and their attributes, possible attribute values depends on the file type represented by the binary.

If the Type is ssh2_pubkey, the result will be Decoded_ssh2_pubkey. Otherwise it will be Decoded_OtherType.

RFC4716 attributes - see RFC 4716.

{headers, [{string(), utf8_string()}]}

auth_key attributes - see manual page for sshd.
{comment, string()}
{options, [string()]}

{bits, integer()} - In SSH version 1 files.

known_host attributes - see manual page for sshd.
{hostnames, [string()]}
{comment, string()}

{bits, integer()} - In SSH version 1 files.

Example: {ok, SshBin} = file:read_file("known_hosts").

If Type is public_key the binary can be either an RFC4716 public key or an OpenSSH public key.


Type = ssh2_pubkey | OtherType
OtherType = public_key | ssh_file()
InData = InData_ssh2_pubkey | OtherInData
InData_ssh2_pubkey = public_key() | ed_legacy_pubkey()
OtherInData = [{Key, Attributes}]
Attributes = [{atom(), term()}]

This function is deprecated and should not be used in new programs. Use ssh_file:encode/2 instead.

Encodes a list of SSH file entries (public keys and attributes) to a binary. Possible attributes depend on the file type, see ssh_decode/2 .

If the Type is ssh2_pubkey, the InData shall be InData_ssh2_pubkey. Otherwise it shall be OtherInData.


HostKey = public_key()
DigestType = digest_type()

Calculates a ssh fingerprint from a public host key as openssh does.


This function is deprecated and should not be used in new programs. Use ssh:hostkey_fingerprint/1 or ssh:hostkey_fingerprint/2 instead.

The algorithm in ssh_hostkey_fingerprint/1 is md5 to be compatible with older ssh-keygen commands. The string from the second variant is prepended by the algorithm name in uppercase as in newer ssh-keygen commands.


 2> public_key:ssh_hostkey_fingerprint(Key).    

 3> public_key:ssh_hostkey_fingerprint(md5,Key).

 4> public_key:ssh_hostkey_fingerprint(sha,Key).

 5> public_key:ssh_hostkey_fingerprint(sha256,Key).

 6> public_key:ssh_hostkey_fingerprint([sha,sha256],Key).


Generates a short hash of an issuer name. The hash is returned as a string containing eight hexadecimal digits.

The return value of this function is the same as the result of the commands openssl crl -hash and openssl x509 -issuer_hash, when passed the issuer name of a CRL or a certificate, respectively. This hash is used by the c_rehash tool to maintain a directory of symlinks to CRL files, in order to facilitate looking up a CRL by its issuer name.