Class: OpenSSL::HMAC

Inherits:
Object
  • Object
show all
Defined in:
ossl_hmac.c,
lib/openssl/hmac.rb,
ossl_hmac.c

Overview

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.new('SHA256')
hmac = OpenSSL::HMAC.new(key, digest)
hmac << data1
hmac << data2
mac = hmac.digest

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#new(key, digest) ⇒ Object

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 can be securely compared with #== in constant time:

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


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# File 'ossl_hmac.c', line 95

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;
}

Class Method Details

.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|x9Bx85xB8xB7x8AxA6xBCx8Az6xF7nx90px1Cx9DxB4xD9”

Returns:

  • (aString)

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# File 'ossl_hmac.c', line 270

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

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”

Returns:

  • (aString)

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# File 'ossl_hmac.c', line 302

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;
}

Instance Method Details

#==(other) ⇒ Object

Securely compare with another HMAC instance in constant time.


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# File '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

#digestString

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+xB0xEExB0x18xEBxBDEx97xAErx13qx1ExC6a`x84?”

Returns:

  • (String)

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# File 'ossl_hmac.c', line 184

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;
}

#hexdigestString Also known as: inspect, to_s

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

Returns:

  • (String)

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# File 'ossl_hmac.c', line 207

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;
}

#initialize_copy(other) ⇒ Object


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# File 'ossl_hmac.c', line 108

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;
}

#resetself

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

Returns:

  • (self)

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# File 'ossl_hmac.c', line 242

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

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

    return self;
}

#update(string) ⇒ self Also known as: <<

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

Returns:

  • (self)

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# File 'ossl_hmac.c', line 142

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;
}