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* cipher.verify -> string

*

* Verifies the decrypted ciphertext against the tag set prior to

* decryption using the ciphertext and optional associated

* authentication data. Returns an empty string if the ciphertext was

* authenticated successfully, otherwise raises an

* OpenSSL::Cipher::CipherError.

*

* Only call this method after setting the authentication tag

* appropriate for your cipher mode and passing the entire contents

* of the ciphertext into the cipher, and before calling

* Cipher#final.

*/

static VALUE

ossl_cipher_verify(VALUE self)

{

EVP_CIPHER_CTX *ctx;

int out_len = 0;

GetCipher(self, ctx);

if (!EVP_CipherUpdate(ctx, NULL, &out_len, NULL, 0))

ossl_raise(eCipherError, "ciphertext failed to authenticate");

return rb_str_new(0, 0);

}

/*

* call-seq:

/*

* call-seq:

* cipher.aad = string -> string

*

* Sets the cipher's additional authenticated data. This field may be

* set optionally before using AEAD cipher modes such as GCM or

* CCM. The contents of this field should be non-sensitive

* data which will be added to the ciphertext to generate the

* authentication tag which validates the contents of the ciphertext.

*

* The AAD must be set prior to encryption or decryption. Only call

* this method after calling Cipher#encrypt when encrypting, and

* after Cipher#decrypt and Cipher#gcm_tag= when decrypting.

*/

static VALUE

ossl_cipher_set_aad(VALUE self, VALUE data)

{

EVP_CIPHER_CTX *ctx;

unsigned char *in = NULL;

int in_len = 0;

int out_len = 0;

StringValue(data);

in = (unsigned char *) RSTRING_PTR(data);

in_len = RSTRING_LENINT(data);

GetCipher(self, ctx);

if (!EVP_CipherUpdate(ctx, NULL, &out_len, in, in_len))

ossl_raise(eCipherError, "couldn't set additional authenticated data");

return self;

}

/*

* call-seq:

* cipher.gcm_tag -> string

*

* Gets the authentication tag generated by GCM cipher modes. This

* tag may be stored along with the ciphertext, then set on the

* decryption cipher to authenticate the contents of the ciphertext

* against changes.

*

* The tag may only be retrieved after calling Cipher#final.

*/

static VALUE

ossl_cipher_get_gcm_tag(VALUE self)

{

EVP_CIPHER_CTX *ctx;

VALUE tag;

// GCM tags are 16 bytes in OpenSSL

tag = rb_str_new(NULL, 16);

GetCipher(self, ctx);

if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, (unsigned char *)RSTRING_PTR(tag)))

ossl_raise(eCipherError, "Cipher#finish must be called before getting the tag");

return tag;

}

/*

* call-seq:

* cipher.gcm_tag = string -> string

*

* Sets the authentication tag to verify the contents of the

* ciphertext. The GCM tag must be set after calling Cipher#decrypt

* but before decrypting any of the ciphertext. After all decryption

* is performed, the tag can be verified by calling Cipher#verify.

*/

static VALUE

ossl_cipher_set_gcm_tag(VALUE self, VALUE data)

{

EVP_CIPHER_CTX *ctx;

unsigned char *in = NULL;

int in_len = 0;

StringValue(data);

in = (unsigned char *) RSTRING_PTR(data);

in_len = RSTRING_LENINT(data);

GetCipher(self, ctx);

if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, in_len, in))

ossl_raise(eCipherError, "unable to set GCM tag");

return data;

}

rb_define_method(cCipher, "verify", ossl_cipher_verify, 0);

rb_define_method(cCipher, "aad=", ossl_cipher_set_aad, 1);

rb_define_method(cCipher, "gcm_tag=", ossl_cipher_set_gcm_tag, 1);

rb_define_method(cCipher, "gcm_tag", ossl_cipher_get_gcm_tag, 0);

if OpenSSL::OPENSSL_VERSION_NUMBER > 0x1000103f

def test_aes_gcm

pt = File.read(__FILE__)

c1 = OpenSSL::Cipher.new('aes-256-gcm')

c2 = OpenSSL::Cipher.new('aes-256-gcm')

c3 = OpenSSL::Cipher.new('aes-256-gcm')

c1.encrypt

c1.pkcs5_keyivgen('passwd')

c1.aad = 'aad'

ct = c1.update(pt) + c1.final

tag = c1.gcm_tag

c2.decrypt

c2.pkcs5_keyivgen('passwd')

c2.gcm_tag = tag

c2.aad = 'aad'

assert_equal(pt, c2.update(ct) + c2.verify + c2.final)

c3.decrypt

c3.pkcs5_keyivgen('passwd')

c3.gcm_tag = tag[0..-2] << tag[-1].succ

c3.aad = 'aad'

assert_raise OpenSSL::Cipher::CipherError do

c3.update(ct) + c3.verify + c3.final

end

end

end