Why are my Java and command line SHA256 outputs different?

Question

I'm getting different outputs from hashing a string on the command line vs. in Java on Android. I'm sure I'm doing something wrong, but I don't see what.

Command line:

kevin@aphrodite:~$ echo derp | sha256sum
ee673d13de31533a375b41d9e57731d9bb4dbddbd6c1d2364f15be40fd783346  -

Java:

final String plaintext = "derp";
final MessageDigest md;
try {
    md = MessageDigest.getInstance("SHA-256");
} catch (NoSuchAlgorithmException e) {
/* SHA-256 should be supported on all devices. */
    throw new RuntimeException(e);
}
final String inputHash = bytesToHex(md.digest(plaintext.getBytes()));
Log.debug(TAG, "input hash: " + inputHash);

Java output:

10-05 13:32:57.412: D/Config(12082): input hash: 3f4146a1d0b5dac26562ff7dc6248573f4e996cf764a0f517318ff398dcfa792

Here's the bytesToHex(...) method, which I found in another Q&A. I confirmed that it's doing the right thing by logging Integer.toHexString(b) for each b.

private static final char[] hexDigit = "0123456789abcdef".toCharArray();

private static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    for (int i = 0; i < bytes.length; ++i) {
        int b = bytes[i] & 0xFF;
        hexChars[i * 2] = hexDigit[b >>> 4];
        hexChars[i * 2 + 1] = hexDigit[b & 0x0F];
    }
    return new String(hexChars);
}

Since the answer has already been established (\n in echo), might I also suggest that you can supplant your custom bytesToHex() in favor of DatatypeConverter.printHexBinary(byte[] val) — Keith
– Keith, Commented Oct 5, 2015 at 20:51

Elliott Frisch · Accepted Answer · 2015-10-05 20:46:33Z

14

Because echo includes a trailing new-line. You can use

echo -n derp | sha256sum

or add \n to your plaintext like

final String plaintext = "derp\n";

answered Oct 5, 2015 at 20:46

Elliott Frisch

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