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(Unicode C) AEAD AES 128-bit GCMDemonstrates AES encryption using the Galois/Counter Mode (GCM). GCM is an authenticated encryption mode with "additional data" (often referred to as AEAD). GCM is a cipher mode that can be applied to any symmetric encryption algorithm with a 16-byte block size, such as AES and Twofish. In GCM mode, the block encryption algorithm is transformed into a stream encryption algorithm, and therefore no padding occurs (and the PaddingScheme property does not apply). The "additional data" (known as the AAD) does not get encrypted but plays a role in the computation of the resulting "authenticated tag".
#include <C_CkCrypt2W.h> void ChilkatSample(void) { HCkCrypt2W crypt; const wchar_t *K; const wchar_t *IV; const wchar_t *AAD; const wchar_t *PT; const wchar_t *CT; const wchar_t *T; BOOL success; const wchar_t *ctResult; const wchar_t *tResult; const wchar_t *ptResult; const wchar_t *tInvalid; // This example assumes the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. crypt = CkCrypt2W_Create(); // Set the encryption algorithm to "AES" CkCrypt2W_putCryptAlgorithm(crypt,L"aes"); // Indicate that the Galois/Counter Mode (GCM) should be used: CkCrypt2W_putCipherMode(crypt,L"gcm"); // KeyLength may be 128, 192, 256 CkCrypt2W_putKeyLength(crypt,128); // This is the 128-bit AES secret key (in hex format) K = L"feffe9928665731c6d6a8f9467308308"; // This is the 16-byte initialization vector: IV = L"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. AAD = L"feedfacedeadbeeffeedfacedeadbeefabaddad2"; // The plain-text bytes (in hex format) to be encrypted. PT = L"d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39"; // The expected cipher text (in hex format) CT = L"42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091"; // The expected authenticated tag given the above inputs. T = L"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". CkCrypt2W_putEncodingMode(crypt,L"hex"); // Set the secret key and IV CkCrypt2W_SetEncodedIV(crypt,IV,L"hex"); CkCrypt2W_SetEncodedKey(crypt,K,L"hex"); // Set the additional authenticated data (AAD) success = CkCrypt2W_SetEncodedAad(crypt,AAD,L"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. ctResult = CkCrypt2W_encryptEncoded(crypt,PT); if (CkCrypt2W_getLastMethodSuccess(crypt) != TRUE) { wprintf(L"%s\n",CkCrypt2W_lastErrorText(crypt)); CkCrypt2W_Dispose(crypt); return; } // Examine the result. It should be the same (case insensitive) as our expected result: wprintf(L"computed result: %s\n",ctResult); wprintf(L"expected result: %s\n",CT); // Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag: tResult = CkCrypt2W_getEncodedAuthTag(crypt,L"hex"); wprintf(L"computed authTag: %s\n",tResult); wprintf(L"expected authTag: %s\n",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 = CkCrypt2W_SetEncodedAuthTag(crypt,T,L"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. ptResult = CkCrypt2W_decryptEncoded(crypt,CT); if (CkCrypt2W_getLastMethodSuccess(crypt) != TRUE) { // Failed. The resultant authenticated tag did not equal the expected authentication tag. wprintf(L"%s\n",CkCrypt2W_lastErrorText(crypt)); CkCrypt2W_Dispose(crypt); return; } // Examine the decrypted result. It should be the same as our expected plaintext (case insensitive) wprintf(L"plaintext decrypted: %s\n",ptResult); wprintf(L"plaintext expected: %s\n",PT); // Let's intentionally set the expected authenticated tag to an incorrect value. // The decrypt operation should fail: tInvalid = L"ffaabbbc3221a5db94fae95ae7121a47"; success = CkCrypt2W_SetEncodedAuthTag(crypt,tInvalid,L"hex"); ptResult = CkCrypt2W_decryptEncoded(crypt,CT); if (CkCrypt2W_getLastMethodSuccess(crypt) != TRUE) { // Failed. The resultant authenticated tag did not equal the expected authentication tag. wprintf(L"%s\n",CkCrypt2W_lastErrorText(crypt)); } CkCrypt2W_Dispose(crypt); } |
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