Class: OpenSSL::HMAC (Ruby 2.5.7)
Description: Class : OpenSSL::HMAC - Ruby 2.5.7

### Home Classes Methods

### In Files

- openssl/ossl.c

### Parent

Object

### Methods

- ::digest
- ::hexdigest
- ::new
- #<<
- #digest
- #hexdigest
- #initialize_copy
- #inspect
- #reset
- #to_s
- #update

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

### Public Class Methods

digest(digest, key, data) → aString click to toggle source

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"

                   static VALUE
    ossl_hmac_s_digest(VALUE klass, VALUE digest, VALUE key, VALUE data)
    {
        unsigned char *buf;
        unsigned int buf_len;

        StringValue(key);
        StringValue(data);
        buf = HMAC(ossl_evp_get_digestbyname(digest), RSTRING_PTR(key),
                   RSTRING_LENINT(key), (unsigned char *)RSTRING_PTR(data),
                   RSTRING_LEN(data), NULL, &buf_len);

        return rb_str_new((const char *)buf, buf_len);
    }

hexdigest(digest, key, data) → aString click to toggle source

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"

                   static VALUE
    ossl_hmac_s_hexdigest(VALUE klass, VALUE digest, VALUE key, VALUE data)
    {
        unsigned char buf[EVP_MAX_MD_SIZE];
        unsigned int buf_len;
        VALUE ret;

        StringValue(key);
        StringValue(data);

        if (!HMAC(ossl_evp_get_digestbyname(digest), RSTRING_PTR(key),
                  RSTRING_LENINT(key), (unsigned char *)RSTRING_PTR(data),
                  RSTRING_LEN(data), buf, &buf_len))
            ossl_raise(eHMACError, "HMAC");

        ret = rb_str_new(NULL, buf_len * 2);
        ossl_bin2hex(buf, RSTRING_PTR(ret), buf_len);

        return ret;
    }

new(key, digest) → hmac click to toggle source

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'
    digest = OpenSSL::Digest.new('sha1')
    instance = OpenSSL::HMAC.new(key, digest)
    #=> f42bb0eeb018ebbd4597ae7213711ec60760843f
    instance.class
    #=> OpenSSL::HMAC

### A note about comparisons¶ ↑

Two instances won't be equal when they're compared, even if they have the same value. Use `to_s` or `hexdigest` to return the authentication code that the instance represents. For example:

    other_instance = OpenSSL::HMAC.new('key', OpenSSL::Digest.new('sha1'))
    #=> f42bb0eeb018ebbd4597ae7213711ec60760843f
    instance
    #=> f42bb0eeb018ebbd4597ae7213711ec60760843f
    instance == other_instance
    #=> false
    instance.to_s == other_instance.to_s
    #=> true

                   static VALUE
    ossl_hmac_initialize(VALUE self, VALUE key, VALUE digest)
    {
        HMAC_CTX *ctx;

        StringValue(key);
        GetHMAC(self, ctx);
        HMAC_Init_ex(ctx, RSTRING_PTR(key), RSTRING_LENINT(key),
                     ossl_evp_get_digestbyname(digest), NULL);

        return self;
    }

### Public Instance Methods

<<(p1) click to toggle source
Alias for: update
digest → string click to toggle source

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

### Example¶ ↑

    instance = OpenSSL::HMAC.new('key', OpenSSL::Digest.new('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)
    {
        HMAC_CTX *ctx;
        unsigned int buf_len;
        VALUE ret;

        GetHMAC(self, ctx);
        ret = rb_str_new(NULL, EVP_MAX_MD_SIZE);
        hmac_final(ctx, (unsigned char *)RSTRING_PTR(ret), &buf_len);
        assert(buf_len <= EVP_MAX_MD_SIZE);
        rb_str_set_len(ret, buf_len);

        return ret;
    }

hexdigest → string click to toggle source

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

                   static VALUE
    ossl_hmac_hexdigest(VALUE self)
    {
        HMAC_CTX *ctx;
        unsigned char buf[EVP_MAX_MD_SIZE];
        unsigned int buf_len;
        VALUE ret;

        GetHMAC(self, ctx);
        hmac_final(ctx, buf, &buf_len);
        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) click to toggle source

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

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

        GetHMAC(self, ctx1);
        GetHMAC(other, ctx2);

        if (!HMAC_CTX_copy(ctx1, ctx2))
            ossl_raise(eHMACError, "HMAC_CTX_copy");
        return self;
    }

inspect() click to toggle source
Alias for: hexdigest
reset → self click to toggle source

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', OpenSSL::Digest.new('sha1'))
    #=> f42bb0eeb018ebbd4597ae7213711ec60760843f

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

                   static VALUE
    ossl_hmac_reset(VALUE self)
    {
        HMAC_CTX *ctx;

        GetHMAC(self, ctx);
        HMAC_Init_ex(ctx, NULL, 0, NULL, NULL);

        return self;
    }

to_s() click to toggle source
Alias for: hexdigest
update(string) → self click to toggle source

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)
    {
        HMAC_CTX *ctx;

        StringValue(data);
        GetHMAC(self, ctx);
        HMAC_Update(ctx, (unsigned char *)RSTRING_PTR(data), RSTRING_LEN(data));

        return self;
    }

Also aliased as: <<