public static void performAESGCM(string text)
{
Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
bool success = crypt.UnlockComponent("Anything for 30-day trial");
if (success != true)
{
Console.WriteLine(crypt.LastErrorText);
return;
}
// Set the encryption algorithm to "AES"
crypt.CryptAlgorithm = "aes";
// Indicate that the Galois/Counter Mode (GCM) should be used:
crypt.CipherMode = "gcm";
// KeyLength may be 128, 192, 256
crypt.KeyLength = 128;
// This is the 128-bit AES secret key (in hex format)
string K = "feffe9928665731c6d6a8f9467308308";
// This is the 16-byte initialization vector:
string IV = "cafebabefacedbaddecaf888";
// This is the additional data to be used as input to the GCM AEAD algorithm,
// but is not included in the output. It plays a role in the computation of the
// resulting authenticated tag.
string AAD = "feedfacedeadbeeffeedfacedeadbeefabaddad2";
// The plain-text bytes (in hex format) to be encrypted.
string PT = "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39";
PT = text;
// The expected cipher text (in hex format)
string CT = "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091";
// The expected authenticated tag given the above inputs.
string T = "5bc94fbc3221a5db94fae95ae7121a47";
// Note: The above data are the values for test vector #4 from
// the PDF document at: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf
// EncodingMode specifies the encoding of the output for
// encryption, and the input for decryption.
// It may be "hex", "url", "base64", or "quoted-printable".
crypt.EncodingMode = "hex";
// Set the secret key and IV
crypt.SetEncodedIV(IV, "hex");
crypt.SetEncodedKey(K, "hex");
// Set the additional authenticated data (AAD)
success = crypt.SetEncodedAad(AAD, "hex");
// For the purpose of duplicating the test vectors, we are using the EncryptEncoded method.
// This method decodes the input string according to the encoding specified by the EncodingMode
// property, which in this case is "hex". The decoded bytes are encrypted using the mode specified
// by the CipherMode property. The resulting
// encrypted bytes are encoded (again using the encoding mode specified by EncodingMode),
// and the result is returned.
// <b>Note:</b> The CipherMode property sets the block mode of operation (gcm, cfb, cbc, ofb, ecb, etc.)
// for any of the Chilkat encryption/decryption methods (such as EncryptBytes, EncryptString,
// CkEncryptFile, etc.) Just because GCM mode is demonstrated with EncryptEncoded/DecryptEncoded,
// does not imply that GCM mode is specific to only these methods.
string ctResult = crypt.EncryptEncoded(PT);
if (crypt.LastMethodSuccess != true)
{
// Console.WriteLine(crypt.LastErrorText);
return;
}
// Examine the result. It should be the same (case insensitive) as our expected result:
// Console.WriteLine("computed result: " + ctResult);
// Console.WriteLine("expected result: " + CT);
// Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
string tResult = crypt.GetEncodedAuthTag("hex");
//Console.WriteLine("computed authTag: " + tResult);
//Console.WriteLine("expected authTag: " + T);
// -------------------------------------------------------------------------------------
// Now let's GCM decrypt...
// -------------------------------------------------------------------------------------
// Before GCM decrypting, we must set the authenticated tag to the value that is expected.
// The decryption will fail if the resulting authenticated tag is not equal (case insensitive) to
// the expected result.
// Note: The return value of SetEncodedAuthTag indicates whether the string passed was a valid
// representation of the encoding specified in the 2nd arg.
success = crypt.SetEncodedAuthTag(T, "hex");
// All of our properties (IV, secret key, cipher mode, and AAD) are already set from the code above...
// So let's decrypt CT to and check to see if we get PT.
string ptResult = crypt.DecryptEncoded(CT);
if (crypt.LastMethodSuccess != true)
{
// Failed. The resultant authenticated tag did not equal the expected authentication tag.
// Console.WriteLine(crypt.LastErrorText);
return;
}
// Examine the decrypted result. It should be the same as our expected plaintext (case insensitive)
//Console.WriteLine("plaintext decrypted: " + ptResult);
//Console.WriteLine("plaintext expected: " + PT);
// Let's intentionally set the expected authenticated tag to an incorrect value.
// The decrypt operation should fail:
string tInvalid = "ffaabbbc3221a5db94fae95ae7121a47";
success = crypt.SetEncodedAuthTag(tInvalid, "hex");
ptResult = crypt.DecryptEncoded(CT);
if (crypt.LastMethodSuccess != true)
{
// Failed. The resultant authenticated tag did not equal the expected authentication tag.
// Console.WriteLine(crypt.LastErrorText);
}
}
