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 as OTP 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 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: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'{}, #'EcpkParameters'{} | {namedCurve, oid()}}

ec_private_key() =


public_crypt_options() =

[{rsa_pad, rsa_padding()}]

rsa_padding() =


| 'rsa_pkcs1_oaep_padding'

| 'rsa_no_padding'

digest_type() =

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

rsa_digest_type() =

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

dss_digest_type() =


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)->


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

Computes 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 ASN.1 specifications.
Der = der_encoded()

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

der_encode(Asn1Type, Entity) -> der_encoded()


Asn1Type = atom()
ASN.1 type present in the Public Key applications ASN.1 specifications.
Entity = term()
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}


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

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()


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.

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").

Decodes PEM binary data and returns 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. 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()


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

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

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


Cert = der_encoded()

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()


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 directly calls der_encode/2.

pkix_is_issuer(Cert, IssuerCert) -> boolean()


Cert = der_encoded() | #'OTPCertificate'{} | #'CertificateList'{}
IssuerCert = der_encoded() | #'OTPCertificate'{}

Checks if IssuerCert issued Cert.

pkix_is_fixed_dh_cert(Cert) -> boolean()


Cert = der_encoded() | #'OTPCertificate'{}

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

pkix_is_self_signed(Cert) -> boolean()


Cert = der_encoded() | #'OTPCertificate'{}

Checks if a certificate is self-signed.

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


Cert = der_encoded() | #'OTPCertificate'{}
IssuedBy = self | other
IssuerID = {integer(), issuer_name()}
The issuer id consists of the serial number and the issuers name.
Reason = term()

Returns the issuer id.

pkix_normalize_name(Issuer) -> Normalized


Issuer = issuer_name()
Normalized = issuer_name()

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}}


TrustedCert = #'OTPCertificate'{} | der_encoded() | 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 is to be run through the verify_fun. Examples are unknown_ca and selfsigned_peer.
CertChain = [der_encoded()]
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 is always 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 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()


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

Returns the issuer of the CRL.

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:

{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}

pkix_crl_verify(CRL, Cert) -> boolean()


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

Verify that Cert is the CRL signer.

pkix_dist_point(Cert) -> DistPoint


Cert = der_encoded() | #'OTPCertificate'{}
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

pkix_dist_points(Cert) -> DistPoints


Cert = der_encoded() | #'OTPCertificate'{}
DistPoints = [#'DistributionPoint'{}]

Extracts distribution points from the certificates extensions.

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


Key = rsa_private_key() | dsa_private_key()

Signs an '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 | ecdsa

Translates signature algorithm OID to Erlang digest and signature types.

pkix_verify(Cert, Key) -> boolean()


Cert = der_encoded()
Key = rsa_public_key() | dsa_public_key() | ec_public_key()

Verifies 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", that is, 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 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()


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

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 .

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", that is, 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.