Method decrypt

security/src/main/java/pro/tools/security/sm/SM2.java:271–329

私钥解密 @param encryptData 密文数据字节数组 @param privateKey 解密私钥 @return

(byte[] encryptData, BigInteger privateKey)

     * @return
     */
    public String decrypt(byte[] encryptData, BigInteger privateKey) {

        byte[] C1Byte = new byte[65];
        System.arraycopy(encryptData, 0, C1Byte, 0, C1Byte.length);

        ECPoint C1 = curve.decodePoint(C1Byte).normalize();

        /*
         * 计算椭圆曲线点 S = [h]C1 是否为无穷点
         */
        BigInteger h = ecc_bc_spec.getH();
        if (h != null) {
            ECPoint S = C1.multiply(h);
            if (S.isInfinity()) {
                throw new IllegalStateException();
            }
        }
        /* 计算[dB]C1 = (x2, y2) */
        ECPoint dBC1 = C1.multiply(privateKey).normalize();

        /* 计算t = KDF(x2 || y2, klen) */
        byte[] dBC1Bytes = dBC1.getEncoded(false);
        int klen = encryptData.length - 65 - DIGEST_LENGTH;
        byte[] t = KDF(dBC1Bytes, klen);
        // DerivationFunction kdf = new KDF1BytesGenerator(new
        // ShortenedDigest(new SHA256Digest(), DIGEST_LENGTH));
        // if (debug)
        // System.out.println("klen = " + klen);
        // kdf.init(new ISO18033KDFParameters(dBC1Bytes));
        // kdf.generateBytes(t, 0, t.length);

        if (allZero(t)) {
            System.err.println("all zero");
            throw new IllegalStateException();
        }

        /* 5 计算M'=C2^t */
        byte[] M = new byte[klen];
        for (int i = 0; i < M.length; i++) {
            M[i] = (byte) (encryptData[C1Byte.length + i] ^ t[i]);
        }
        /* 6 计算 u = Hash(x2 || M' || y2) 判断 u == C3是否成立 */
        byte[] C3 = new byte[DIGEST_LENGTH];

        System.arraycopy(encryptData, encryptData.length - DIGEST_LENGTH, C3, 0, DIGEST_LENGTH);
        byte[] u = sm3hash(dBC1.getXCoord().toBigInteger().toByteArray(), M,
                dBC1.getYCoord().toBigInteger().toByteArray());
        if (Arrays.equals(u, C3)) {
            try {
                return new String(M, "UTF8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return null;
        } else {
            return null;
        }