Java Different MD5 output for same input?

Question

My code to generate md5 looks like

@Nonnull
static String getAuthCode(@Nonnull final String email, @Nonnull final String memberExternalId,
                          @Nonnull final String clientId, @Nonnull final String clientSecret) {
    final MessageDigest messageDigest = getMessageDigest("MD5");
    final String stringForHashCode = email + ":" + memberExternalId + ":" + clientId + ":" + clientSecret;
    messageDigest.update(stringForHashCode.getBytes());
    return new BigInteger(1, messageDigest.digest()).toString();
}

I run the test as

@Test
public void test() {
    System.out.println(getAuthCode("a", "b", "c", "d"));
}

and I get the output as

306937959255909402080036399104389354327

When I run the same test on online website, I get the output as

e6ea19c62a3763c7b78c475652c51357

for same input a:b:c:d

Question

Why are they different?
How can I get the output similar to what I get online? which is e6ea19c62a3763c7b78c475652c51357?

messageDigest.update(stringForHashCode.getBytes()); <-- this will use the default JVM encoding. Is that what you want? Rule of thumb: always specify the encoding! — fge
– fge, Commented Jan 1, 2015 at 20:49
Not sure what encoding will give me result similar to what I get online — daydreamer
– daydreamer, Commented Jan 1, 2015 at 20:51
I even tried messageDigest.update(stringForHashCode.getBytes(Charset.forName("UTF-8"))); but the result is still the same — daydreamer
– daydreamer, Commented Jan 1, 2015 at 20:53

Jon Skeet · Accepted Answer · 2015-01-01 20:56:35Z

3

The problem pointed out in comments is a problem - you should define which encoding you want to use. I'd recommend using UTF-8, e.g.

messageDigest.update(stringForHashCode.getBytes(StandardCharsets.UTF_8));

A bigger problem, however, is that you're printing out a BigInteger created from the digest - which is printing it out in decimal. The result you're getting from the online tool is in hexadecimal instead.

While you could convert the BigInteger into hex, I would personally avoid creating a BigInteger in the first place - you'd need to work out padding etc. Instead, just use one of the many libraries available for converting a byte[] to hex, e.g. Apache Commons Codec with its Hex class.

answered Jan 1, 2015 at 20:56

Jon Skeet

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1 Comment

Louis Wasserman Over a year ago

Guava's Hashing.md5().hashString(str, UTF_8).toString() also prints out hex.

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