Sha256 Hashes in Kotlin

Our first example demonstrates how to compute SHA256 hashes in Kotlin. SHA256 hashes are frequently used to compute short identities for binary or text blobs. For example, TLS/SSL certificates use SHA256 to compute a certificate’s signature.

import java.security.MessageDigest

fun main() {
    val s = "sha256 this string"

    // Here we start with a new hash.
    val md = MessageDigest.getInstance("SHA-256")

    // update expects bytes. If you have a string s,
    // use s.toByteArray() to convert it to bytes.
    md.update(s.toByteArray())

    // This gets the finalized hash result as a byte array.
    val bs = md.digest()

    println(s)
    println(bs.joinToString("") { "%02x".format(it) })
}

Kotlin implements several hash functions in the java.security package, which we can access through the MessageDigest class.

Running the program computes the hash and prints it in a human-readable hex format.

$ kotlinc SHA256Hashes.kt -include-runtime -d SHA256Hashes.jar
$ java -jar SHA256Hashes.jar
sha256 this string
1af1dfa857bf1d8814fe1af8983c18080019922e557f15a8a...

You can compute other hashes using a similar pattern to the one shown above. For example, to compute SHA512 hashes, you would use MessageDigest.getInstance("SHA-512").

Note that if you need cryptographically secure hashes, you should carefully research hash strength!