Module Summary

API module for public-key infrastructure.


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

Data types


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:


The following data types are used in the functions for public_key:


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

boolean() =

true | false

string() =


der_encoded() =


pki_asn1_type() =


| 'RSAPrivateKey'

| 'RSAPublicKey'

| 'DSAPrivateKey'

| 'DSAPublicKey'

| 'DHParameter'

| 'SubjectPublicKeyInfo'

| 'PrivateKeyInfo'

| 'CertificationRequest'

| 'CertificateList'

| 'ECPrivateKey'

| 'EcpkParameters'

pem_entry () =

{pki_asn1_type(), binary(), %% DER or encrypted DER

not_encrypted | cipher_info()}

cipher_info() =

{"RC2-CBC" | "DES-CBC" | "DES-EDE3-CBC", crypto:strong_rand_bytes(8)

| {#'PBEParameter{}, digest_type()} | #'PBES2-params'{}}

public_key() =

rsa_public_key() | dsa_public_key() | ec_public_key()

private_key() =

rsa_private_key() | dsa_private_key() | ec_private_key()

rsa_public_key() =


rsa_private_key() =


dsa_public_key() =

{integer(), #'Dss-Parms'{}}

dsa_private_key() =



= {#'ECPoint'{}, #'ECParameters'{} | {namedCurve, oid()}}

ec_private_key() =


key_params() =

#'DHParameter'{} | {namedCurve, oid()} | #'ECParameters'{} | {rsa, Size::integer(), PubExp::integer()}

public_crypt_options() =

[{rsa_pad, rsa_padding()}]

rsa_padding() =


| 'rsa_pkcs1_oaep_padding'

| 'rsa_no_padding'

public_sign_options() =

[{rsa_pad, rsa_sign_padding()} | {rsa_pss_saltlen, integer()}]

rsa_sign_padding() =


| 'rsa_pkcs1_pss_padding'

digest_type() =

Union of rsa_digest_type(), dss_digest_type(), and ecdsa_digest_type().

rsa_digest_type() =

'md5' | 'ripemd160' | 'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

dss_digest_type() =

'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

Note that the actual supported dss_digest_type depends on the underlying crypto library. In OpenSSL version >= 1.0.1 the listed digest are supported, while in 1.0.0 only sha, sha224 and sha256 are supported. In version 0.9.8 only sha is supported.

ecdsa_digest_type() =

'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

crl_reason() =


| keyCompromise

| cACompromise

| affiliationChanged

| superseded

| cessationOfOperation

| certificateHold

| privilegeWithdrawn

| aACompromise

issuer_name() =


ssh_file() =


| rfc4716_public_key

| known_hosts

| auth_keys


compute_key(OthersKey, MyKey)->compute_key(OthersKey, MyKey, Params)->


Computes shared secret.

decrypt_private(CipherText, Key) -> binary()decrypt_private(CipherText, Key, Options) -> binary()


Public-key decryption using the private key. See also crypto:private_decrypt/4

decrypt_public(CipherText, Key) - > binary()decrypt_public(CipherText, Key, Options) - > binary()


Public-key decryption using the public key. See also crypto:public_decrypt/4

der_decode(Asn1type, Der) -> term()


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

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

der_encode(Asn1Type, Entity) -> der_encoded()


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

Erlang representation of Asn1Type

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

dh_gex_group(MinSize, SuggestedSize, MaxSize, Groups) -> {ok, {Size,Group}} | {error,Error}


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 

encrypt_private(PlainText, Key) -> binary()


Public-key encryption using the private key. See also crypto:private_encrypt/4.

encrypt_public(PlainText, Key) -> binary()


Public-key encryption using the public key. See also crypto:public_encrypt/4.

generate_key(Params) -> {Public::binary(), Private::binary()} | #'ECPrivateKey'{} | #'RSAPrivateKey'{}


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

pem_decode(PemBin) -> [pem_entry()]


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

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

pem_encode(PemEntries) -> binary()


Creates a PEM binary.

pem_entry_decode(PemEntry) -> term()pem_entry_decode(PemEntry, Password) -> term()


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().

pem_entry_encode(Asn1Type, Entity) -> pem_entry()pem_entry_encode(Asn1Type, Entity, {CipherInfo, Password}) -> pem_entry()


Erlang representation of Asn1Type. 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.

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

pkix_decode_cert(Cert, otp|plain) -> #'Certificate'{} | #'OTPCertificate'{}


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.

pkix_encode(Asn1Type, Entity, otp | plain) -> der_encoded()


The ASN.1 type can be 'Certificate', 'OTPCertificate' or a subtype of either.

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.

pkix_is_issuer(Cert, IssuerCert) -> boolean()


Checks if IssuerCert issued Cert.

pkix_is_fixed_dh_cert(Cert) -> boolean()


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

pkix_is_self_signed(Cert) -> boolean()


Checks if a certificate is self-signed.

pkix_issuer_id(Cert, IssuedBy) -> {ok, IssuerID} | {error, Reason}


The issuer id consists of the serial number and the issuers name.

Returns the issuer id.

pkix_normalize_name(Issuer) -> Normalized


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

pkix_path_validation(TrustedCert, CertChain, Options) -> {ok, {PublicKeyInfo, PolicyTree}} | {error, {bad_cert, Reason}}


Normally a trusted certificate, but it can also be a path-validation error that can be discovered while constructing the input to this function and that is to be run through the verify_fun. Examples are unknown_ca and selfsigned_peer.

A list of DER-encoded certificates in trust order ending with the peer certificate.

At the moment this is always an empty list as policies are not currently supported.

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.

Available options:

{verify_fun, fun()}

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.

{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.

Possible 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.

pkix_crl_issuer(CRL) -> issuer_name()


Returns the issuer of the CRL.

pkix_crls_validate(OTPCertificate, DPAndCRLs, Options) -> CRLStatus()


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 can not be determined, and this option is set to true, details of why no CRLs where accepted are included in the return value.

pkix_crl_verify(CRL, Cert) -> boolean()


Verify that Cert is the CRL signer.

pkix_dist_point(Cert) -> DistPoint


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

pkix_dist_points(Cert) -> DistPoints


Extracts distribution points from the certificates extensions.

pkix_match_dist_point(CRL, DistPoint) -> boolean()


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.

pkix_sign(#'OTPTBSCertificate'{}, Key) -> der_encoded()


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

pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}


Signature OID from a certificate or a certificate revocation list.

Translates signature algorithm OID to Erlang digest and signature types.

pkix_test_data(Options) -> Configpkix_test_data([chain_opts()]) -> [conf_opt()]


Options for ROOT, Intermediate and Peer certs

A valid chain must have at least a ROOT and a peer cert. The root cert can be given either as a cert pre-generated by pkix_test_root_cert/2, or as root cert generation options. A root certificate generated by pkix_test_root_cert/2. For available options see cert_opt() below. This is a subset of the type ssl:ssl_option(). PrivateKey is what generate_key/1 returns.

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.

The cert_opt() type consists of the following options:

{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 can not be used to achieve real security. This function is provided for testing purposes only.

pkix_test_root_cert(Name, Options) -> RootCert


The root certificate name.

For available options see cert_opt() under pkix_test_data/1. A root certificate and key. The Key is generated by generate_key/1.

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.

pkix_verify(Cert, Key) -> boolean()


Verifies PKIX x.509 certificate signature.

pkix_verify_hostname(Cert, ReferenceIDs) -> boolean()pkix_verify_hostname(Cert, ReferenceIDs, Opts) -> boolean()


This function checks that the Presented Identifier (e.g hostname) in a peer certificate is in agreement with 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 Manual and code examples describes this function more detailed.

The {OtherRefId,term()} is defined by the user and is passed to the match_fun, if defined. If that term is a binary, it will be converted to a string.

The ip Reference ID takes an inet:ip_address() or an ip address in string format (E.g "" or "1234::5678:9012") as second element.

sign(Msg, DigestType, Key) -> binary()sign(Msg, DigestType, Key, Options) -> binary()


The Msg is either the binary "plain text" data to be signed or it is the hashed value of "plain text", that is, the digest.

Creates a digital signature.

ssh_decode(SshBin, Type) -> [{public_key(), Attributes::list()}]


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.

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.

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.

ssh_encode([{Key, Attributes}], Type) -> binary()


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.

ssh_hostkey_fingerprint(HostKey) -> string()ssh_hostkey_fingerprint(DigestType, HostKey) -> string()ssh_hostkey_fingerprint([DigestType], HostKey) -> [string()]


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

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).

verify(Msg, DigestType, Signature, Key) -> boolean()verify(Msg, DigestType, Signature, Key, Options) -> boolean()


The Msg is either the binary "plain text" data or it is the hashed value of "plain text", that is, the digest.

Verifies a digital signature.

short_name_hash(Name) -> string()


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.

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Licensed under the Apache License, Version 2.0.