# 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
Source

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

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="

digest(digest, key, data) → aString
Source

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

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"

hexdigest(digest, key, data) → aString
Source

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

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"

new(key, digest) → hmac
Source

    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;
    }

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

### Public Instance Methods

<<
Alias for: update
== (other)
Source

    # 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

Securely compare with another `HMAC` instance in constant time.

base64digest → string
Source

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

Returns the authentication code an a Base64-encoded string.

digest → string
Source

    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;
    }

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?"

hexdigest → string
Source

    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;
    }

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

Also aliased as: inspect, to_s
initialize_copy (p1)
Source

    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
Source

    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;
    }

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

to_s
Alias for: hexdigest
update(string) → self
Source

    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;
    }

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

Also aliased as: <<