Example usage for org.bouncycastle.crypto.modes CFBBlockCipher decryptBlock

Introduction

In this page you can find the example usage for org.bouncycastle.crypto.modes CFBBlockCipher decryptBlock.

Prototype

public int decryptBlock(byte[] in, int inOff, byte[] out, int outOff)
        throws DataLengthException, IllegalStateException 

Source Link

Document

Do the appropriate processing for CFB mode decryption.

Usage

From source file:me.grapebaba.hyperledger.fabric.Crypto.java

License:Apache License

public ByteString eciesDecrypt(PrivateKey recipientPrivateKey, ByteString cipherText) {
    BCECPrivateKey bcecPrivateKey = (BCECPrivateKey) recipientPrivateKey;
    ECNamedCurveSpec ecNamedCurveSpec = (ECNamedCurveSpec) bcecPrivateKey.getParams();
    int level = SecurityLevel.from(ecNamedCurveSpec.getName()).size();

    //cipherText = ephemeralPubKeyBytes + encryptedTokBytes + macBytes
    //ephemeralPubKeyBytes = first ((384+7)/8)*2 + 1 bytes = first 97 bytes
    //hmac is sha3_384 = 48 bytes or sha3_256 = 32 bytes
    int ephemeralPubKeyLength = ((level + 7) / 8) * 2 + 1;
    int hmacLength = level >> 3;
    int cipherTextLength = cipherText.size();

    if (cipherTextLength <= ephemeralPubKeyLength + hmacLength)
        throw new RuntimeException(String.format("Illegal cipherText length: %d must be > %d", cipherTextLength,
                ephemeralPubKeyLength + hmacLength));

    ByteString ephemeralPubKey = cipherText.substring(0, ephemeralPubKeyLength);
    ByteString encryptedContent = cipherText.substring(ephemeralPubKeyLength, cipherTextLength - hmacLength);
    ByteString hmac = cipherText.substring(cipherTextLength - hmacLength);

    ECPrivateKeyParameters ecdhPrivateKeyParameters;
    try {/*www . j a  v  a2s .  c  o  m*/
        ecdhPrivateKeyParameters = (ECPrivateKeyParameters) (PrivateKeyFactory
                .createKey(bcecPrivateKey.getEncoded()));
    } catch (IOException e) {
        logger.error("ECIES decrypt load private key exception", e);
        throw new RuntimeException(e);
    }
    ECDomainParameters ecDomainParameters = ecdhPrivateKeyParameters.getParameters();
    ECCurve ecCurve = ecDomainParameters.getCurve();
    ECPublicKeyParameters ecPublicKeyParameters = new ECPublicKeyParameters(
            ecCurve.decodePoint(ephemeralPubKey.toByteArray()), ecDomainParameters);
    BasicAgreement agree = new ECDHBasicAgreement();
    agree.init(ecdhPrivateKeyParameters);
    byte[] keyAgreement = agree.calculateAgreement(ecPublicKeyParameters).toByteArray();

    HKDFParameters hkdfParameters = new HKDFParameters(keyAgreement, null, null);
    HKDFBytesGenerator hkdfBytesGenerator = new HKDFBytesGenerator(digest);
    hkdfBytesGenerator.init(hkdfParameters);
    byte[] hkdfOutputBytes = new byte[AESKEY_LENGTH + HMACKEY_LENGTH];
    hkdfBytesGenerator.generateBytes(hkdfOutputBytes, 0, AESKEY_LENGTH + HMACKEY_LENGTH);
    ByteString hkdfOutput = ByteString.copyFrom(hkdfOutputBytes);
    ByteString aesKey = hkdfOutput.substring(0, AESKEY_LENGTH);
    ByteString hmacKey = hkdfOutput.substring(AESKEY_LENGTH, AESKEY_LENGTH + HMACKEY_LENGTH);
    HMac hMac = new HMac(digest);
    hMac.init(new KeyParameter(hmacKey.toByteArray()));
    hMac.update(encryptedContent.toByteArray(), 0, encryptedContent.size());
    byte[] recoveredHmac = new byte[hMac.getMacSize()];
    hMac.doFinal(recoveredHmac, 0);
    if (!MessageDigest.isEqual(hmac.toByteArray(), recoveredHmac)) {
        throw new RuntimeException("HMAC verify failed");
    }

    CFBBlockCipher aesCipher = new CFBBlockCipher(new AESEngine(), BLOCK_BIT_SIZE);
    ByteString iv = encryptedContent.substring(0, IV_LENGTH);
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(aesKey.toByteArray()), iv.toByteArray());
    aesCipher.init(false, ivAndKey);
    byte[] decryptedBytes = new byte[500];
    aesCipher.decryptBlock(encryptedContent.substring(IV_LENGTH).toByteArray(), 0, decryptedBytes, 0);
    return ByteString.copyFrom(decryptedBytes);
}

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