class OpenSSL::HMAC

OpenSSL::HMAC allows computing Hash-based Message Authentication Code (HMAC). It is a type of message authentication code (MAC) involving a hash function in combination with a key. HMAC can be used to verify the integrity of a message as well as the authenticity.

OpenSSL::HMAC has a similar interface to OpenSSL::Digest.

HMAC-SHA256 using one-shot interface¶ ↑

key = "key"
data = "message-to-be-authenticated"
mac = OpenSSL::HMAC.hexdigest("SHA256", key, data)
#=> "cddb0db23f469c8bf072b21fd837149bd6ace9ab771cceef14c9e517cc93282e"

HMAC-SHA256 using incremental interface¶ ↑

data1 = File.binread("file1")
data2 = File.binread("file2")
key = "key"
hmac = OpenSSL::HMAC.new(key, 'SHA256')
hmac << data1
hmac << data2
mac = hmac.digest

Public Class Methods

base64digest(digest, key, data) → aString

Returns the authentication code as a Base64-encoded string. The digest parameter specifies the digest algorithm to use. This may be a String representing the algorithm name or an instance of OpenSSL::Digest.

Example¶ ↑

key = 'key'
data = 'The quick brown fox jumps over the lazy dog'

hmac = OpenSSL::HMAC.base64digest('SHA1', key, data)
#=> "3nybhbi3iqa8ino29wqQcBydtNk="

# File ext/openssl/lib/openssl/hmac.rb, line 73
def base64digest(digest, key, data)
  [digest(digest, key, data)].pack("m0")
end

digest(digest, key, data) → aString

Returns the authentication code as a binary string. The digest parameter specifies the digest algorithm to use. This may be a String representing the algorithm name or an instance of OpenSSL::Digest.

Example¶ ↑

key = 'key'
data = 'The quick brown fox jumps over the lazy dog'

hmac = OpenSSL::HMAC.digest('SHA1', key, data)
#=> "\xDE|\x9B\x85\xB8\xB7\x8A\xA6\xBC\x8Az6\xF7\n\x90p\x1C\x9D\xB4\xD9"

# File ext/openssl/lib/openssl/hmac.rb, line 35
def digest(digest, key, data)
  hmac = new(key, digest)
  hmac << data
  hmac.digest
end

hexdigest(digest, key, data) → aString

Returns the authentication code as a hex-encoded string. The digest parameter specifies the digest algorithm to use. This may be a String representing the algorithm name or an instance of OpenSSL::Digest.

Example¶ ↑

key = 'key'
data = 'The quick brown fox jumps over the lazy dog'

hmac = OpenSSL::HMAC.hexdigest('SHA1', key, data)
#=> "de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9"

# File ext/openssl/lib/openssl/hmac.rb, line 54
def hexdigest(digest, key, data)
  hmac = new(key, digest)
  hmac << data
  hmac.hexdigest
end

new(key, digest) → hmac

Returns an instance of OpenSSL::HMAC set with the key and digest algorithm to be used. The instance represents the initial state of the message authentication code before any data has been processed. To process data with it, use the instance method update with your data as an argument.

Example¶ ↑

key = 'key'
instance = OpenSSL::HMAC.new(key, 'SHA1')
#=> f42bb0eeb018ebbd4597ae7213711ec60760843f
instance.class
#=> OpenSSL::HMAC

A note about comparisons¶ ↑

Two instances can be securely compared with == in constant time:

    other_instance = OpenSSL::HMAC.new('key', 'SHA1')
#=> f42bb0eeb018ebbd4597ae7213711ec60760843f
instance == other_instance
#=> true

static VALUE
ossl_hmac_initialize(VALUE self, VALUE key, VALUE digest)
{
    EVP_MD_CTX *ctx;
    EVP_PKEY *pkey;

    GetHMAC(self, ctx);
    StringValue(key);
#ifdef HAVE_EVP_PKEY_NEW_RAW_PRIVATE_KEY
    pkey = EVP_PKEY_new_raw_private_key(EVP_PKEY_HMAC, NULL,
                                        (unsigned char *)RSTRING_PTR(key),
                                        RSTRING_LENINT(key));
    if (!pkey)
        ossl_raise(eHMACError, "EVP_PKEY_new_raw_private_key");
#else
    pkey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL,
                                (unsigned char *)RSTRING_PTR(key),
                                RSTRING_LENINT(key));
    if (!pkey)
        ossl_raise(eHMACError, "EVP_PKEY_new_mac_key");
#endif
    if (EVP_DigestSignInit(ctx, NULL, ossl_evp_get_digestbyname(digest),
                           NULL, pkey) != 1) {
        EVP_PKEY_free(pkey);
        ossl_raise(eHMACError, "EVP_DigestSignInit");
    }
    /* Decrement reference counter; EVP_MD_CTX still keeps it */
    EVP_PKEY_free(pkey);

    return self;
}

Public Instance Methods

Alias for: update

== (other)

Securely compare with another HMAC instance in constant time.

# File ext/openssl/lib/openssl/hmac.rb, line 6
def ==(other)
  return false unless HMAC === other
  return false unless self.digest.bytesize == other.digest.bytesize

  OpenSSL.fixed_length_secure_compare(self.digest, other.digest)
end

base64digest → string

Returns the authentication code an a Base64-encoded string.

# File ext/openssl/lib/openssl/hmac.rb, line 17
def base64digest
  [digest].pack("m0")
end

digest → string

Returns the authentication code an instance represents as a binary string.

Example¶ ↑

instance = OpenSSL::HMAC.new('key', 'SHA1')
#=> f42bb0eeb018ebbd4597ae7213711ec60760843f
instance.digest
#=> "\xF4+\xB0\xEE\xB0\x18\xEB\xBDE\x97\xAEr\x13q\x1E\xC6\a`\x84?"

static VALUE
ossl_hmac_digest(VALUE self)
{
    EVP_MD_CTX *ctx;
    size_t buf_len = EVP_MAX_MD_SIZE;
    VALUE ret;

    GetHMAC(self, ctx);
    ret = rb_str_new(NULL, EVP_MAX_MD_SIZE);
    if (EVP_DigestSignFinal(ctx, (unsigned char *)RSTRING_PTR(ret),
                            &buf_len) != 1)
        ossl_raise(eHMACError, "EVP_DigestSignFinal");
    rb_str_set_len(ret, (long)buf_len);

    return ret;
}

hexdigest → string

Returns the authentication code an instance represents as a hex-encoded string.

static VALUE
ossl_hmac_hexdigest(VALUE self)
{
    EVP_MD_CTX *ctx;
    unsigned char buf[EVP_MAX_MD_SIZE];
    size_t buf_len = EVP_MAX_MD_SIZE;
    VALUE ret;

    GetHMAC(self, ctx);
    if (EVP_DigestSignFinal(ctx, buf, &buf_len) != 1)
        ossl_raise(eHMACError, "EVP_DigestSignFinal");
    ret = rb_str_new(NULL, buf_len * 2);
    ossl_bin2hex(buf, RSTRING_PTR(ret), buf_len);

    return ret;
}

Also aliased as: inspect, to_s

initialize_copy (p1)

static VALUE
ossl_hmac_copy(VALUE self, VALUE other)
{
    EVP_MD_CTX *ctx1, *ctx2;

    rb_check_frozen(self);
    if (self == other) return self;

    GetHMAC(self, ctx1);
    GetHMAC(other, ctx2);
    if (EVP_MD_CTX_copy(ctx1, ctx2) != 1)
        ossl_raise(eHMACError, "EVP_MD_CTX_copy");
    return self;
}

inspect

Alias for: hexdigest

reset → self

Returns hmac as it was when it was first initialized, with all processed data cleared from it.

Example¶ ↑

data = "The quick brown fox jumps over the lazy dog"
instance = OpenSSL::HMAC.new('key', 'SHA1')
#=> f42bb0eeb018ebbd4597ae7213711ec60760843f

instance.update(data)
#=> de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9
instance.reset
#=> f42bb0eeb018ebbd4597ae7213711ec60760843f

static VALUE
ossl_hmac_reset(VALUE self)
{
    EVP_MD_CTX *ctx;
    EVP_PKEY *pkey;

    GetHMAC(self, ctx);
    pkey = EVP_PKEY_CTX_get0_pkey(EVP_MD_CTX_get_pkey_ctx(ctx));
    if (EVP_DigestSignInit(ctx, NULL, EVP_MD_CTX_get0_md(ctx), NULL, pkey) != 1)
        ossl_raise(eHMACError, "EVP_DigestSignInit");

    return self;
}

to_s

Alias for: hexdigest

update(string) → self

Returns hmac updated with the message to be authenticated. Can be called repeatedly with chunks of the message.

Example¶ ↑

first_chunk = 'The quick brown fox jumps '
second_chunk = 'over the lazy dog'

instance.update(first_chunk)
#=> 5b9a8038a65d571076d97fe783989e52278a492a
instance.update(second_chunk)
#=> de7c9b85b8b78aa6bc8a7a36f70a90701c9db4d9

static VALUE
ossl_hmac_update(VALUE self, VALUE data)
{
    EVP_MD_CTX *ctx;

    StringValue(data);
    GetHMAC(self, ctx);
    if (EVP_DigestSignUpdate(ctx, RSTRING_PTR(data), RSTRING_LEN(data)) != 1)
        ossl_raise(eHMACError, "EVP_DigestSignUpdate");

    return self;
}

Also aliased as: <<