Hash a string in Java emulating the php function hash_hmac using ripemd160 with a key

Question

I'm trying to hash a String in Java using ripemd160 to emulate the output of the following php:

$string = 'string';
$key = 'test';

hash_hmac('ripemd160', $string, $key);

// outputs: 37241f2513c60ae4d9b3b8d0d30517445f451fa5

Attempt 1

Initially I'd tried to emulate it using the following... however I don't believe it's possible to use ripemd160 as a getInstance` algorithm?

Or maybe it is and I just don't have it locally enabled?

public String signRequest(String uri, String secret) {
    try {

        byte[] keyBytes = secret.getBytes();           
        SecretKeySpec signingKey = new SecretKeySpec(keyBytes, "HmacSHA1");

        Mac mac = Mac.getInstance("ripemd160");
        mac.init(signingKey);

        // Compute the hmac on input data bytes
        byte[] rawHmac = mac.doFinal(uri.getBytes());

        // Convert raw bytes to Hex
        byte[] hexBytes = new Hex().encode(rawHmac);

        //  Covert array of Hex bytes to a String
        return new String(hexBytes, "UTF-8");
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
} 

Attempt 2

This led me to look for other ways to accomplish the above, through SO and Google I found that looking at BouncyCastle may be a better way to go.

I then found this post that talks about hashing using the same algorithm as I'd like and also BouncyCastle, it just doesn't use a key. (Cannot output correct hash in Java. What is wrong?)

public static String toRIPEMD160(String in) {
    try {
        byte[] addr = in.getBytes();
        byte[] out = new byte[20];
        RIPEMD160Digest digest = new RIPEMD160Digest();

        byte[] rawSha256 = sha256(addr);
        String encodedSha256 = getHexString(rawSha256);
        byte[] strBytes = base64Sha256.getBytes("UTF-8");
        digest.update(strBytes, 0, strBytes.length);

        digest.doFinal(out, 0);
        return getHexString(out);
    } catch (UnsupportedEncodingException ex) {
        return null;
    }
}

I have this working as it would be expected to.

Issue

You'll note that in attempt 2 there is currently no way to supply a key for the hashing, my question is how can I adapt this function to be able to supply a key and accomplish the last stage of what I need to do to be able to emulate the original php function: hash_hmac('ripemd160', $string, $key);

Answer 1

Using RIPEMD160 from Bouncy Castle is fine, but you'll have to implement HMAC, not just hash your data. HMac it just H(K XOR opad, H(K XOR ipad, text)), where H is your hash function, K is the secret, text the message and opad and ipad are predefined constants. To demonstrate how it works, I translated the following from Python's implementation:

public static String signRequest(String uri, String secret) throws Exception {
    byte[] r = uri.getBytes("US-ASCII");

    // The keys must have the same block size as your hashing algorithm, in this case
    // 64 bytes right-padded with zeros.
    byte[] k_outer = new byte[64];
    System.arraycopy(secret.getBytes("US-ASCII"), 0, k_outer, 0,
        secret.getBytes("US-ASCII").length);
    byte[] k_inner = new byte[64];
    System.arraycopy(secret.getBytes("US-ASCII"), 0, k_inner, 0, 
        secret.getBytes("US-ASCII").length);

    // You'll create two nested hashes. The inner one is initialized with the
    // key xor 0x36 (byte-wise), the other one with the key xor 0x5c.
    for(int i=0; i<k_outer.length; i++)
        k_outer[i] ^= 0x5c;
    for(int i=0; i<k_inner.length; i++)
        k_inner[i] ^= 0x36;

    // Update inner hash with the key and data you want to sign
    RIPEMD160Digest d_inner = new RIPEMD160Digest();
    d_inner.update(k_inner, 0, k_inner.length);
    d_inner.update(r, 0, r.length);

    // Update outer hash with the key and the inner hash 
    RIPEMD160Digest d_outer = new RIPEMD160Digest();
    d_outer.update(k_outer, 0, k_outer.length);

    byte[] o_inner = new byte[d_inner.getDigestSize()];
    d_inner.doFinal(o_inner, 0);
    d_outer.update(o_inner, 0, o_inner.length);

    // Finally, return the hex-encoded hash
    byte[] o_outer = new byte[d_inner.getDigestSize()];
    d_outer.doFinal(o_outer, 0);

    return new String((new Hex()).encode(o_outer), "US-ASCII");
}

Bouncy Castle implements this algorithm in its HMac class, so a shorter variant of this code is

public static String signRequest(String uri, String secret) throws Exception {
    byte[] r = uri.getBytes("US-ASCII");
    byte[] k = secret.getBytes("US-ASCII");

    HMac hmac = new HMac(new RIPEMD160Digest());
    hmac.init(new KeyParameter(k));
    hmac.update(r, 0, r.length);

    byte[] out = new byte[hmac.getMacSize()];
    hmac.doFinal(out, 0);

    return new String((new Hex()).encode(out), "US-ASCII");
}