API module for public key infrastructure.

This module provides functions to handle public key infrastructure. It can encode/decode different file formats (PEM, openssh), sign and verify digital signatures and validate certificate paths and certificate revocation lists.


public_key requires the crypto and asn1 applications, the latter since R16 (hopefully the runtime dependency on asn1 will be removed again in the future). Supports RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile Supports PKCS-1 - RSA Cryptography Standard Supports DSS- Digital Signature Standard (DSA - Digital Signature Algorithm) Supports PKCS-3 - Diffie-Hellman Key Agreement Standard Supports PKCS-5 - Password-Based Cryptography Standard Supports PKCS-8 - Private-Key Information Syntax Standard Supports PKCS-10 - Certification Request Syntax Standard



All records used in this manual are generated from ASN.1 specifications and are documented in the User's Guide. See Public key records and X.509 Certificate records.

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


Data Types

oid() - Object Identifier, a tuple of integers as generated by the ASN1 compiler.

boolean() = true | false

string() = [bytes()]

der_encoded() = binary()

pki_asn1_type() = 'Certificate' | 'RSAPrivateKey'| 'RSAPublicKey' | 'DSAPrivateKey' | 'DSAPublicKey' | 'DHParameter' | 'SubjectPublicKeyInfo' | 'PrivateKeyInfo' | 'CertificationRequest' | '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: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() = #'RSAPublicKey'{}

rsa_private_key() = #'RSAPrivateKey'{}

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

dsa_private_key() = #'DSAPrivateKey'{}

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

ec_private_key() = #'ECPrivateKey'{}

public_crypt_options() = [{rsa_pad, rsa_padding()}].

rsa_padding() = 'rsa_pkcs1_padding' | 'rsa_pkcs1_oaep_padding' | 'rsa_no_padding'

digest_type() - Union of below digest types

rsa_digest_type() = 'md5' | 'sha' | 'sha224' | 'sha256' | 'sha384' | 'sha512'

dss_digest_type() = 'sha'

ecdsa_digest_type() = 'sha'| 'sha224' | 'sha256' | 'sha384' | 'sha512'

crl_reason() = unspecified | keyCompromise | cACompromise | affiliationChanged | superseded | cessationOfOperation | certificateHold | privilegeWithdrawn | aACompromise

ssh_file() = openssh_public_key | rfc4716_public_key | known_hosts | auth_keys


compute_key(OthersKey, MyKey)->

compute_key(OthersKey, MyKey, Params)->

  • OthersKey = #'ECPoint'{} | binary(), MyKey = #'ECPrivateKey'{} | binary()
  • Params = #'DHParameter'{}

Compute shared secret

decrypt_private(CipherText, Key) -> binary()

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

  • CipherText = binary()
  • Key = rsa_private_key()
  • Options = public_crypt_options()

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

decrypt_public(CipherText, Key) - > binary()

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

  • CipherText = binary()
  • Key = rsa_public_key()
  • Options = public_crypt_options()

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

der_decode(Asn1type, Der) -> term()

  • Asn1Type = atom()
  • ASN.1 type present in the public_key applications asn1 specifications.
  • Der = der_encoded()

Decodes a public key ASN.1 DER encoded entity.

der_encode(Asn1Type, Entity) -> der_encoded()

  • Asn1Type = atom()
  • Asn1 type present in the public_key applications ASN.1 specifications.
  • Entity = term()
  • The erlang representation of Asn1Type

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

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

  • Params = #'DHParameter'{} | {namedCurve, oid()} | #'ECParameters'{}

Generates a new keypair

pem_decode(PemBin) -> [pem_entry()]

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

Decode PEM binary data and return entries as ASN.1 DER encoded entities.

pem_encode(PemEntries) -> binary()

  • PemEntries = [pem_entry()]

Creates a PEM binary

pem_entry_decode(PemEntry) -> term()

pem_entry_decode(PemEntry, Password) -> term()

  • PemEntry = pem_entry()
  • Password = string()

Decodes a PEM entry. pem_decode/1 returns a list of PEM entries. Note that if the PEM entry is of type 'SubjectPublickeyInfo' it will be 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()

  • Asn1Type = pki_asn1_type()
  • Entity = term()
  • The Erlang representation of Asn1Type. If Asn1Type is 'SubjectPublicKeyInfo' then Entity must be either an rsa_public_key() or a dsa_public_key() and this function will create the appropriate 'SubjectPublicKeyInfo' entry.
  • CipherInfo = cipher_info()
  • Password = string()

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

encrypt_private(PlainText, Key) -> binary()

  • PlainText = binary()
  • Key = rsa_private_key()

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

encrypt_public(PlainText, Key) -> binary()

  • PlainText = binary()
  • Key = rsa_public_key()

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

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

  • Cert = der_encoded()

Decodes an ASN.1 DER encoded PKIX certificate. The otp option will use 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()

  • Asn1Type = atom()
  • The ASN.1 type can be 'Certificate', 'OTPCertificate' or a subtype of either .
  • Entity = #'Certificate'{} | #'OTPCertificate'{} | a valid subtype

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 will directly call der_encode/2.

pkix_is_issuer(Cert, IssuerCert) -> boolean()

  • Cert = der_encode() | #'OTPCertificate'{}
  • IssuerCert = der_encode() | #'OTPCertificate'{}

Checks if IssuerCert issued Cert

pkix_is_fixed_dh_cert(Cert) -> boolean()

  • Cert = der_encode() | #'OTPCertificate'{}

Checks if a Certificate is a fixed Diffie-Hellman Cert.

pkix_is_self_signed(Cert) -> boolean()

  • Cert = der_encode() | #'OTPCertificate'{}

Checks if a Certificate is self signed.

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

  • Cert = der_encode() | #'OTPCertificate'{}
  • IssuedBy = self | other
  • IssuerID = {integer(), {rdnSequence, [#'AttributeTypeAndValue'{}]}}
  • The issuer id consists of the serial number and the issuers name.
  • Reason = term()

Returns the issuer id.

pkix_normalize_name(Issuer) -> Normalized

  • Issuer = {rdnSequence,[#'AttributeTypeAndValue'{}]}
  • Normalized = {rdnSequence, [#'AttributeTypeAndValue'{}]}

Normalizes a 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}}

  • TrustedCert = #'OTPCertificate'{} | der_encode() | atom()
  • 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 should be run through the verify_fun. For example unknown_ca or selfsigned_peer
  • CertChain = [der_encode()]
  • A list of DER encoded certificates in trust order ending with the peer certificate.
  • Options = proplists:proplist()
  • PublicKeyInfo = {?'rsaEncryption' | ?'id-dsa', rsa_public_key() | integer(), 'NULL' | 'Dss-Parms'{}}
  • PolicyTree = term()
  • At the moment this will always be an empty list as Policies are not currently supported
  • Reason = cert_expired | invalid_issuer | invalid_signature | name_not_permitted | missing_basic_constraint | invalid_key_usage | {revoked, crl_reason()} | atom()

Performs a basic path validation according to RFC 5280. However CRL validation is done separately by pkix_crls_validate/3 and should be called from the supplied verify_fun

Available options are:

{verify_fun, fun()}

The fun should 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} should be used.

{max_path_length, integer()}
The max_path_length is the maximum number of non-self-issued intermediate certificates that may 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 1 the path can be PEER, CA, ROOT-CA, if it is 2 PEER, CA, CA, ROOT-CA and so on.

Possible reasons for a bad certificate are:

The certificate is no longer valid as its expiration date has passed.
The certificate issuer name does not match the name of the issuer certificate in the chain.
The 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 should be checked by the verify_fun

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

  • OTPCertificate = #'OTPCertificate'{}
  • DPAndCRLs = [{DP::#'DistributionPoint'{}, {DerCRL::der_encoded(), CRL::#'CertificateList'{}}}]
  • Options = proplists:proplist()
  • CRLStatus() = valid | {bad_cert, revocation_status_undetermined} | {bad_cert, {revoked, crl_reason()}}

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

Available options are:

{update_crl, fun()}

The fun has the following type spec:

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

The fun should use the information in the distribution point to acesses the lates possible version of the CRL. If this fun is not specified public_key will use the default implementation:

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

The fun has the following type spec:

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

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

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

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

  • Key = rsa_public_key() | dsa_public_key()

Signs a 'OTPTBSCertificate'. Returns the corresponding der encoded certificate.

pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}

  • AlgorithmId = oid()
  • Signature oid from a certificate or a certificate revocation list
  • DigestType = rsa_digest_type() | dss_digest_type()
  • SignatureType = rsa | dsa

Translates signature algorithm oid to erlang digest and signature types.

pkix_verify(Cert, Key) -> boolean()

  • Cert = der_encode()
  • Key = rsa_public_key() | dsa_public_key()

Verify PKIX x.509 certificate signature.

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

  • Msg = binary() | {digest,binary()}
  • The msg is either the binary "plain text" data to be signed or it is the hashed value of "plain text" i.e. the digest.
  • DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
  • Key = rsa_private_key() | dsa_private_key() | ec_private_key()

Creates a digital signature.

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

  • SshBin = binary()
  • Example {ok, SshBin} = file:read_file("known_hosts").
  • Type = public_key | ssh_file()
  • If Type is public_key the binary may be either a rfc4716 public key or a openssh public key.

Decodes a ssh file-binary. In the case of know_hosts or auth_keys the binary may 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 man sshd
{comment, string()} {options, [string()]} {bits, integer()} - In ssh version 1 files
known_host attributes - see man sshd
{hostnames, [string()]} {comment, string()} {bits, integer()} - In ssh version 1 files

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

  • Key = public_key()
  • Attributes = list()
  • Type = ssh_file()

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

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

  • Msg = binary() | {digest,binary()}
  • The msg is either the binary "plain text" data or it is the hashed value of "plain text" i.e. the digest.
  • DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
  • Signature = binary()
  • Key = rsa_public_key() | dsa_public_key() | ec_public_key()

Verifies a digital signature