Generating a base64 encoded hash from CLI to match Java

Question

I have a java code base that generates an URL safe base64 encoded hash from a string, and wondering if / how this would be possible with linux command line tools. I'm guessing the problem with what I am doing here is with the character set / encoding or to do with converting the string to a byte array. Java code:

MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] digest = md.digest("testString".getBytes());
// ^^ this is where the difference is?
String b64url = Base64.encodeBase64URLSafeString(digest);
// b64url: Ss8LOdnEdmcJo2ifVTrAGrVQVF_6RUTfwLLOqC-6AqM

Command line:

echo testString | sha256sum | cut -d" " -f1 | base64
# NDgxOGEyY2JkODYwOTY1NjJkODFmYzIwNmQ3ZTYyNWVlNGFjMTU5MmViNTc0MjQwMDQ4OTIzOTBl
# MDQzZTNlYwo=

Is it possible to generate base64 encoded sha256 via cli tools?

Answer 1

You're base64 encoding a hexadecimal string, not the byte values of the hash, which is the equivalent of:

MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] digest = md.digest("testString".getBytes()); // Missing charset
String hex = Hex.encodeHexString(digest);
String base64 = Base64.encodeBase64(hex.getBytes());

Answer 2

You can use a StringBuilder to turn your hex into a meaningful string:

MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] digest = md.digest("testString".getBytes());
StringBuilder sb = new StringBuuilder();
for (byte b : digest) {
    sb.append(Integer.toHexString(b & 0xff));
}
String base64 = Base64.encodeBase64(sb.toString());

Combined with not including the newline in the echo command, works here ...