This section describes examples of how to use the Public Key API. Keys and certificates used in the following sections are generated only for testing the Public Key application.
Some shell printouts in the following examples are abbreviated for increased readability.
Public-key data (keys, certificates, and so on) can be stored in Privacy Enhanced Mail (PEM) format. The PEM files have the following structure:
<text>
-----BEGIN <SOMETHING>-----
<Attribute> : <Value>
<Base64 encoded DER data>
-----END <SOMETHING>-----
<text>
A file can contain several
A DSA private key can look as follows:
File handling is not done by the Public Key application.
1> {ok, PemBin} = file:read_file("dsa.pem").
{ok,<<"-----BEGIN DSA PRIVATE KEY-----\nMIIBuw"...>>}
The following PEM file has only one entry, a private DSA key:
2> [DSAEntry] = public_key:pem_decode(PemBin).
[{'DSAPrivateKey',<<48,130,1,187,2,1,0,2,129,129,0,183,
179,230,217,37,99,144,157,21,228,204,
162,207,61,246,...>>,
not_encrypted}]
3> Key = public_key:pem_entry_decode(DSAEntry).
#'DSAPrivateKey'{version = 0,
p = 12900045185019966618...6593,
q = 1216700114794736143432235288305776850295620488937,
g = 10442040227452349332...47213,
y = 87256807980030509074...403143,
x = 510968529856012146351317363807366575075645839654}
An RSA private key encrypted with a password can look as follows:
1> {ok, PemBin} = file:read_file("rsa.pem").
{ok,<<"Bag Attribut"...>>}
The following PEM file has only one entry, a private RSA key:
2>[RSAEntry] = public_key:pem_decode(PemBin).
[{'RSAPrivateKey',<<224,108,117,203,152,40,15,77,128,126,
221,195,154,249,85,208,202,251,109,
119,120,57,29,89,19,9,...>>,
{"DES-EDE3-CBC",<<"kÙeø¼pµL">>}}]
In this following example, the password is
3> Key = public_key:pem_entry_decode(RSAEntry, "abcd1234").
#'RSAPrivateKey'{version = 'two-prime',
modulus = 1112355156729921663373...2737107,
publicExponent = 65537,
privateExponent = 58064406231183...2239766033,
prime1 = 11034766614656598484098...7326883017,
prime2 = 10080459293561036618240...77738643771,
exponent1 = 77928819327425934607...22152984217,
exponent2 = 36287623121853605733...20588523793,
coefficient = 924840412626098444...41820968343,
otherPrimeInfos = asn1_NOVALUE}
The following is an example of X509 certificates:
1> {ok, PemBin} = file:read_file("cacerts.pem").
{ok,<<"-----BEGIN CERTIFICATE-----\nMIIC7jCCAl"...>>}
The following file includes two certificates:
2> [CertEntry1, CertEntry2] = public_key:pem_decode(PemBin).
[{'Certificate',<<48,130,2,238,48,130,2,87,160,3,2,1,2,2,
9,0,230,145,97,214,191,2,120,150,48,13,
...>>,
not_encrypted},
{'Certificate',<<48,130,3,200,48,130,3,49,160,3,2,1,2,2,1,
1,48,13,6,9,42,134,72,134,247,...>>>,
not_encrypted}]
Certificates can be decoded as usual:
2> Cert = public_key:pem_entry_decode(CertEntry1).
#'Certificate'{
tbsCertificate =
#'TBSCertificate'{
version = v3,serialNumber = 16614168075301976214,
signature =
#'AlgorithmIdentifier'{
algorithm = {1,2,840,113549,1,1,5},
parameters = <<5,0>>},
issuer =
{rdnSequence,
[[#'AttributeTypeAndValue'{
type = {2,5,4,3},
value = <<19,8,101,114,108,97,110,103,67,65>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,11},
value = <<19,10,69,114,108,97,110,103,32,79,84,80>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,10},
value = <<19,11,69,114,105,99,115,115,111,110,32,65,66>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,7},
value = <<19,9,83,116,111,99,107,104,111,108,109>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,6},
value = <<19,2,83,69>>}],
[#'AttributeTypeAndValue'{
type = {1,2,840,113549,1,9,1},
value = <<22,22,112,101,116,101,114,64,101,114,...>>}]]},
validity =
#'Validity'{
notBefore = {utcTime,"080109082929Z"},
notAfter = {utcTime,"080208082929Z"}},
subject =
{rdnSequence,
[[#'AttributeTypeAndValue'{
type = {2,5,4,3},
value = <<19,8,101,114,108,97,110,103,67,65>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,11},
value = <<19,10,69,114,108,97,110,103,32,79,84,80>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,10},
value = <<19,11,69,114,105,99,115,115,111,110,32,...>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,7},
value = <<19,9,83,116,111,99,107,104,111,108,...>>}],
[#'AttributeTypeAndValue'{
type = {2,5,4,6},
value = <<19,2,83,69>>}],
[#'AttributeTypeAndValue'{
type = {1,2,840,113549,1,9,1},
value = <<22,22,112,101,116,101,114,64,...>>}]]},
subjectPublicKeyInfo =
#'SubjectPublicKeyInfo'{
algorithm =
#'AlgorithmIdentifier'{
algorithm = {1,2,840,113549,1,1,1},
parameters = <<5,0>>},
subjectPublicKey =
{0,<<48,129,137,2,129,129,0,203,209,187,77,73,231,90,...>>}},
issuerUniqueID = asn1_NOVALUE,
subjectUniqueID = asn1_NOVALUE,
extensions =
[#'Extension'{
extnID = {2,5,29,19},
critical = true,
extnValue = [48,3,1,1,255]},
#'Extension'{
extnID = {2,5,29,15},
critical = false,
extnValue = [3,2,1,6]},
#'Extension'{
extnID = {2,5,29,14},
critical = false,
extnValue = [4,20,27,217,65,152,6,30,142|...]},
#'Extension'{
extnID = {2,5,29,17},
critical = false,
extnValue = [48,24,129,22,112,101,116,101|...]}]},
signatureAlgorithm =
#'AlgorithmIdentifier'{
algorithm = {1,2,840,113549,1,1,5},
parameters = <<5,0>>},
signature =
<<163,186,7,163,216,152,63,47,154,234,139,73,154,96,120,
165,2,52,196,195,109,167,192,...>>}
Parts of certificates can be decoded with
public_key:der_decode('X520CommonName', <<19,8,101,114,108,97,110,103,67,65>>).
{printableString,"erlangCA"}
However, certificates can also be decoded using
3>{_, DerCert, _} = CertEntry1.
4> public_key:pkix_decode_cert(DerCert, otp).
#'OTPCertificate'{
tbsCertificate =
#'OTPTBSCertificate'{
version = v3,serialNumber = 16614168075301976214,
signature =
#'SignatureAlgorithm'{
algorithm = {1,2,840,113549,1,1,5},
parameters = 'NULL'},
issuer =
{rdnSequence,
[[#'AttributeTypeAndValue'{
type = {2,5,4,3},
value = {printableString,"erlangCA"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,11},
value = {printableString,"Erlang OTP"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,10},
value = {printableString,"Ericsson AB"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,7},
value = {printableString,"Stockholm"}}],
[#'AttributeTypeAndValue'{type = {2,5,4,6},value = "SE"}],
[#'AttributeTypeAndValue'{
type = {1,2,840,113549,1,9,1},
value = "peter@erix.ericsson.se"}]]},
validity =
#'Validity'{
notBefore = {utcTime,"080109082929Z"},
notAfter = {utcTime,"080208082929Z"}},
subject =
{rdnSequence,
[[#'AttributeTypeAndValue'{
type = {2,5,4,3},
value = {printableString,"erlangCA"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,11},
value = {printableString,"Erlang OTP"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,10},
value = {printableString,"Ericsson AB"}}],
[#'AttributeTypeAndValue'{
type = {2,5,4,7},
value = {printableString,"Stockholm"}}],
[#'AttributeTypeAndValue'{type = {2,5,4,6},value = "SE"}],
[#'AttributeTypeAndValue'{
type = {1,2,840,113549,1,9,1},
value = "peter@erix.ericsson.se"}]]},
subjectPublicKeyInfo =
#'OTPSubjectPublicKeyInfo'{
algorithm =
#'PublicKeyAlgorithm'{
algorithm = {1,2,840,113549,1,1,1},
parameters = 'NULL'},
subjectPublicKey =
#'RSAPublicKey'{
modulus =
1431267547247997...37419,
publicExponent = 65537}},
issuerUniqueID = asn1_NOVALUE,
subjectUniqueID = asn1_NOVALUE,
extensions =
[#'Extension'{
extnID = {2,5,29,19},
critical = true,
extnValue =
#'BasicConstraints'{
cA = true,pathLenConstraint = asn1_NOVALUE}},
#'Extension'{
extnID = {2,5,29,15},
critical = false,
extnValue = [keyCertSign,cRLSign]},
#'Extension'{
extnID = {2,5,29,14},
critical = false,
extnValue = [27,217,65,152,6,30,142,132,245|...]},
#'Extension'{
extnID = {2,5,29,17},
critical = false,
extnValue = [{rfc822Name,"peter@erix.ericsson.se"}]}]},
signatureAlgorithm =
#'SignatureAlgorithm'{
algorithm = {1,2,840,113549,1,1,5},
parameters = 'NULL'},
signature =
<<163,186,7,163,216,152,63,47,154,234,139,73,154,96,120,
165,2,52,196,195,109,167,192,...>>}
This call is equivalent to
5> public_key:pkix_decode_cert(DerCert, plain).
#'Certificate'{ ...}
If you have public-key data and want to create a PEM file
this can be done by calling functions
The second element of the PEM-entry is the ASN.1
1> PemEntry = public_key:pem_entry_encode('RSAPublicKey', RSAPubKey).
{'RSAPublicKey', <<48,72,...>>, not_encrypted}
2> PemBin = public_key:pem_encode([PemEntry]).
<<"-----BEGIN RSA PUBLIC KEY-----\nMEgC...>>
3> file:write_file("rsa_pub_key.pem", PemBin).
ok
or:
1> PemEntry = public_key:pem_entry_encode('SubjectPublicKeyInfo', RSAPubKey).
{'SubjectPublicKeyInfo', <<48,92...>>, not_encrypted}
2> PemBin = public_key:pem_encode([PemEntry]).
<<"-----BEGIN PUBLIC KEY-----\nMFw...>>
3> file:write_file("pub_key.pem", PemBin).
ok
Suppose you have the following private key and a corresponding public key:
Then you can proceed as follows:
Encrypt with the private key:
RsaEncrypted = public_key:encrypt_private(Msg, PrivateKey),
Msg = public_key:decrypt_public(RsaEncrypted, PublicKey),
Encrypt with the public key:
RsaEncrypted = public_key:encrypt_public(Msg, PublicKey),
Msg = public_key:decrypt_private(RsaEncrypted, PrivateKey),
You normally do only one of the encrypt or decrypt operations, and the peer does the other. This normaly used in legacy applications as a primitive digital signature.
Suppose you have the following private key and a corresponding public key:
Then you can proceed as follows:
Signature = public_key:sign(Msg, sha, PrivateKey),
true = public_key:verify(Msg, sha, Signature, PublicKey),
You normally do only one of the sign or verify operations, and the peer does the other.
It can be appropriate to calculate the message digest before
calling
Digest = crypto:sha(Msg),
Signature = public_key:sign(Digest, none, PrivateKey),
true = public_key:verify(Digest, none, Signature, PublicKey),
SSH typically uses PEM files for private keys but has its
own file format for storing public keys. The
RFC 4716 SSH files looks confusingly like PEM files, but there are some differences:
1> {ok, SshBin} = file:read_file("ssh2_rsa_pub").
{ok, <<"---- BEGIN SSH2 PUBLIC KEY ----\nAAAA"...>>}
This is equivalent to calling
2> public_key:ssh_decode(SshBin, public_key).
[{#'RSAPublicKey'{modulus = 794430685...91663,
publicExponent = 35}, []}]
OpenSSH public-key format looks as follows:
1> {ok, SshBin} = file:read_file("openssh_dsa_pub").
{ok,<<"ssh-dss AAAAB3Nza"...>>}
This is equivalent to calling
2> public_key:ssh_decode(SshBin, public_key).
[{{15642692...694280725,
#'Dss-Parms'{p = 17291273936...696123221,
q = 1255626590179665817295475654204371833735706001853,
g = 10454211196...480338645}},
[{comment,"dhopson@VMUbuntu-DSH"}]}]
Known hosts - OpenSSH format looks as follows:
1> {ok, SshBin} = file:read_file("known_hosts").
{ok,<<"hostname.domain.com,192.168.0.1 ssh-rsa AAAAB...>>}
Returns a list of public keys and their related attributes. Each pair of key and attribute corresponds to one entry in the known hosts file:
2> public_key:ssh_decode(SshBin, known_hosts).
[{#'RSAPublicKey'{modulus = 1498979460408...72721699,
publicExponent = 35},
[{hostnames,["hostname.domain.com","192.168.0.1"]}]},
{#'RSAPublicKey'{modulus = 14989794604088...2721699,
publicExponent = 35},
[{comment,"foo@bar.com"},
{hostnames,["|1|BWO5qDxk/cFH0wa05JLdHn+j6xQ=|rXQvIxh5cDD3C43k5DPDamawVNA="]}]}]
Authorized keys - OpenSSH format looks as follows:
1> {ok, SshBin} = file:read_file("auth_keys").
{ok, <<"command=\"dump /home\",no-pty,no-port-forwarding ssh-rsa AAA...>>}
Returns a list of public keys and their related attributes. Each pair of key and attribute corresponds to one entry in the authorized key file:
2> public_key:ssh_decode(SshBin, auth_keys).
[{#'RSAPublicKey'{modulus = 794430685...691663,
publicExponent = 35},
[{comment,"dhopson@VMUbuntu-DSH"},
{options,["command=\"dump/home\"","no-pty",
"no-port-forwarding"]}]},
{{1564269258491...607694280725,
#'Dss-Parms'{p = 17291273936185...763696123221,
q = 1255626590179665817295475654204371833735706001853,
g = 10454211195705...60511039590076780999046480338645}},
[{comment,"dhopson@VMUbuntu-DSH"}]}]
If you got a public key
N> SshBin = public_key:ssh_encode([{PubKey, Attributes}], openssh_public_key),
<<"ssh-rsa "...>>
N+1> file:write_file("id_rsa.pub", SshBin).
ok