How to handle IV / Nonce / Counter for ATR CTR?

Question

import javax.crypto.Cipher;

public abstract class Crypto {


    private static final String CIPHER_ALGORITHM = "AES/CTR/NoPadding";
    private String AesKeyString = "ByWelFHCgFqivFZrWs89LQ==";

    private void setKey() throws NoSuchAlgorithmException{
        byte[] keyBytes;
        keyBytes = Base64.getDecoder().decode(AesKeyString);
        aesKey = new SecretKeySpec(keyBytes, "AES");
    }

    protected byte[] execute(int mode, byte[] target, byte[] iv) 
            throws Exception{
        Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
        IvParameterSpec ivSpec = new IvParameterSpec(iv);
        cipher.init(mode, aesKey, ivSpec);
        return cipher.doFinal(target);
    }

}

In accordance with NIST Recommendation - Appendix B, there are two valid approaches for building the initial blocks of a counter (AES is a 128-bit cipher block):

• 128-bit nonce XORed with an m-bit counter value (typically 32 bits).
• A 64-bit nonce added to a 64-bit counter.

My question is:

• What is the exact procedure for using the initial counting block in the javax.crypto.Cipher instance "AES / CTR / NoPadding" (assuming SunJCE is a provider)? That is, taking into account the above code, which of the previous approaches for the original counter block is used, if any?

Answer 1

Java , . CTR, 16- IV, .

, 128 . , , , . , 32- XOR ( FFFFFFFF, 33- ).

8- nonce , . , , GCM.

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:

Cipher aesCTR = Cipher.getInstance("AES/CTR/NoPadding");
SecretKey aesKey = new SecretKeySpec(new byte[16], "AES");
IvParameterSpec lastIV = new IvParameterSpec(Hex.decode("FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF"));
aesCTR.init(Cipher.ENCRYPT_MODE, aesKey, lastIV);
byte[] twoBlocks = aesCTR.doFinal(new byte[2 * aesCTR.getBlockSize()]);
byte[] secondBlock = Arrays.copyOfRange(twoBlocks, 16, 32);
System.out.printf("%s%n", Hex.toHexString(secondBlock));

IvParameterSpec firstIV = new IvParameterSpec(new byte[16]); // all zero IV
aesCTR.init(Cipher.ENCRYPT_MODE, aesKey, firstIV);
byte[] oneBlock = aesCTR.doFinal(new byte[aesCTR.getBlockSize()]);
System.out.printf("%s%n", Hex.toHexString(oneBlock));

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66e94bd4ef8a2c3b884cfa59ca342b2e
66e94bd4ef8a2c3b884cfa59ca342b2e