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public_key
Reference Manual
Version 0.18

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# public_key

### MODULE

public_key

### MODULE SUMMARY

API module for public key infrastructure.

### DESCRIPTION

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

- public_key requires the crypto application.
- Supports RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
- Supports PKCS-1 - RSA Cryptography Standard
- Supports 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

### COMMON DATA TYPES

Note

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.

     -include_lib("public_key/include/public_key.hrl").

Data Types

    boolean() = true | false

    string() = [bytes()]

    der_encoded() = binary()

    pki_asn1_type() = 'Certificate' | 'RSAPrivateKey'| 'RSAPublicKey' |
        'DSAPrivateKey' | 'DSAPublicKey' | 'DHParameter' | 'SubjectPublicKeyInfo' |
        'PrivateKeyInfo' | 'CertificationRequest'

    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)} |
        'PBES2-params'}

    rsa_public_key()  = #'RSAPublicKey'{}

    rsa_private_key() = #'RSAPrivateKey'{}

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

    dsa_private_key() = #'DSAPrivateKey'{}

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

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

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

     dss_digest_type()  = 'sha'

     crl_reason()  = unspecified | keyCompromise | cACompromise | affiliationChanged | superseded | cessationOfOperation | certificateHold | privilegeWithdrawn |  aACompromise

     ssh_file()  = openssh_public_key | rfc4716_public_key |
        known_hosts | auth_keys

### EXPORTS

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

Types:

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

Public key decryption using the private key.

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

Types:

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

Public key decryption using the public key.

der_decode(Asn1type, Der) -> term()

Types:

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()

Types:

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.

pem_decode(PemBin) -> [pem_entry()]

Types:

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()

Types:

PemEntries = [pem_entry()]

Creates a PEM binary

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

Types:

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()

Types:

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()

Types:

PlainText = binary()
Key = rsa_private_key()

Public key encryption using the private key.

encrypt_public(PlainText, Key) -> binary()

Types:

PlainText = binary()
Key = rsa_public_key()

Public key encryption using the public key.

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

Types:

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()

Types:

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()

Types:

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

Checks if IssuerCert issued Cert

pkix_is_fixed_dh_cert(Cert) -> boolean()

Types:

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

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

pkix_is_self_signed(Cert) -> boolean()

Types:

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

Checks if a Certificate is self signed.

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

Types:

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

Types:

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}}

Types:

TrustedCert = #'OTPCertificate'{} | der_encode() | unknown_ca | selfsigned_peer
Normally a trusted certificate but it can also be one of the path validation errors unknown_ca or selfsigned_peer that can be discovered while constructing the input to this function and that should be run through the verify_fun.
CertChain = [der_encode()]
A list of DER encoded certificates in trust order ending with the peer certificate.
Options = proplists:proplists()
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 | unknown_ca | selfsigned_peer | name_not_permitted | missing_basic_constraint | invalid_key_usage | crl_reason()

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()} |
      	                                     {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.

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

Types:

OTPCertificate = #'OTPCertificate'{}
DPAndCRLs = [{DP::#'DistributionPoint'{} ,CRL::#'CertificateList'{}}]
Options = proplists:proplists()
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

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

Types:

Key = rsa_public_key() | dsa_public_key()

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

pkix_verify(Cert, Key) -> boolean()

Types:

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

Verify PKIX x.509 certificate signature.

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

Types:

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()
Key = rsa_private_key() | dsa_private_key()

Creates a digital signature.

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

Types:

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()

Types:

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()

Types:

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()
Signature = binary()
Key = rsa_public_key() | dsa_public_key()

Verifies a digital signature