Hash of byte array in Java

Question

I'm converting some C# to Java. The C# is:

// Return a SHA256 hash of a string, formatted in hex
private static string HashPassword(string password)
{
    SHA256Managed hash = new SHA256Managed();
    byte[] utf8 = UTF8Encoding.UTF8.GetBytes(password);
    return BytesToHex(hash.ComputeHash(utf8));
}

In Java I replaced SHA256Managed with MessageDigest:

private static String HashPassword(String password)
{
    MessageDigest hash = MessageDigest.getInstance("SHA-256");
    byte[] utf8 = hash.digest(password.getBytes(StandardCharsets.UTF_8));

    return BytesToHex(hash.ComputeHash(utf8)); // ComputeHash?
}

but MessageDigest does not have ComputeHash() nor do I see its equivalent. Is MessageDigest the correct class to use here? If so, what do I do for ComputeHash(). If not what class do I use?

Note that BytesToHex Converts a byte array to a hex string.

Did you read the Javadoc for MessageDigest? The method to finalize the hash is digest() for a hash calculated in several segments, or digest(byte[]) for a single-segment calculation (or as the final segment of a multi-segment hash). — Jim Garrison
– Jim Garrison, Commented Dec 14, 2016 at 20:20

Sam · Accepted Answer · 2016-12-14 20:23:20Z

4

MessageDigest is stateful. You pass data to it incrementally, and call digest() to compute the hash over all the data when you're done.

The hash.digest(byte[]) method you're calling is essentially a shorthand for hash.update(byte[]) then hash.digest().

Calling digest() also resets the MessageDigest instance to its initial state.

answered Dec 14, 2016 at 20:23

Sam

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weston · Accepted Answer · 2016-12-14 20:21:41Z

2

In your Java, the variable utf8 contains your computed hash unlike the C#. To match the way the C# looks it should be:

byte[] utf8 = password.getBytes(StandardCharsets.UTF_8);

return bytesToHex(hash.digest(utf8));

Side note: Please respect Java coding standards with respect to lowerCamelCased method names.

answered Dec 14, 2016 at 20:21

weston

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