如何使用Node.Js解密从Android（Java）发送的数据

Question

I have run into a problem - an existing program uses the code below to encrypt data

public static String encryptData(String data, final String key) {
    try {
        byte[] kb=key.getBytes("utf-8");
        byte[] dig= MessageDigest.getInstance("SHA-1").digest(kb);
        byte[] kdig= Arrays.copyOf(dig, 24);
        final SecretKeySpec secretKeySpec = new SecretKeySpec(kdig, "DESede");

        final Cipher instance = Cipher.getInstance("DESede");
        instance.init(ENCRYPT_MODE, secretKeySpec);

        byte[] ecb=instance.doFinal(data.getBytes("utf-8"));
        byte[] enb64=Base64.encode(ecb, Base64.DEFAULT);
        return new String(enb64);
    } catch (Exception ex) {
        ErmsLogger.e(TAG, ex.getMessage());
        return null;
    }
}

I need to write code on Node.Js that decrypts this encrypted data. So far - I have come up with

function decryptData(encrpted_data,fn){
    var hashedKey = crypto.createHash('sha1').update(config.dataPassword).digest('hex');

    if(hashedKey.length < 48){
        var num=48 - hashedKey.length;
        for(var i=0;i < num; i++){
            hashedKey +='0';
        }
    }

    var key=Buffer.from(hashedKey, 'hex');

    var decipher   = crypto.createDecipher('des-ede', key);
    decoded        = decipher.update(encrpted_data, 'base64', 'utf8');
    decoded       += decipher.final('utf8');
    log.debug(JSON.stringify(decoded));

    return fn(decoded);
}

I keep on running into

Error: error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt
    at Decipher.final (internal/crypto/cipher.js:104:26)

whenever I try to decrypt data sent from the android app. the working decryption code on Android (Java) is

public static String decryptData(final String data, final String password) throws Exception {
        MessageDigest instance=MessageDigest.getInstance("SHA-1");
        byte[] passworddigest=instance.digest(password.getBytes("utf-8"));
        byte[] key=Arrays.copyOf(passworddigest, 24);
        final SecretKeySpec secretKeySpec = new SecretKeySpec(key, "DESede");

        final byte[] decodeddata = Base64.decode(data.getBytes("utf-8"), Base64.DEFAULT);

        final Cipher ciperInstance = Cipher.getInstance("DESede");
        ciperInstance.init(DECRYPT_MODE, secretKeySpec);
        byte[] res= ciperInstance.doFinal(decodeddata);

        return new String(res, "UTF-8");
    }

Could you assist me translate this in Node?

Answer 1

After a bit of research and hitting my head against it - I finally came up with something that works

function decryptData(encrpted_data,fn){

    var encodeKey   = crypto.createHash('sha1').update(config.dataPassword).digest('hex');
    var cryptkey=Buffer.alloc(24);
    encodeKey.copy(cryptkey);

    var decipher = crypto.createDecipheriv('des-ede3', cryptkey,'');
    decipher.setAutoPadding(true);
    decoded  = decipher.update(encrpted_data, 'base64', 'utf8');
    decoded += decipher.final('utf8');

    log.debug(JSON.stringify(decoded));

    return fn(decoded);
}

the explanation - crypto.createDecipher() - internally uses the MD5 hash for the key passed to it and so it really doesn't matter what key value you send in - it will be changed. So the best option is to use createDecipheriv which accepts a raw key. This allows you to hash your key outside before passing it in. Since I was not using any IV - I passed the value of ''. In Java (Android) DESede is really TripleDES and the equivalent on on crypto is 'des-ede3' and not 'des-ede'. I hope this saves someone a couple of hours.