SHA-256 Hashing in Java

1. Overview

The SHA (Secure Hash Algorithm) is one of the popular cryptographic hash functions. A cryptographic hash can be used to make a signature for a text or a data file.

The SHA-256 algorithm generates an almost-unique, fixed-size 256-bit (32-byte) hash. This is a one-way function, so the result cannot be decrypted back to the original value.

Currently, SHA-2 hashing is widely used as it is being considered as the most secure hashing algorithm in the cryptographic arena.

In this article, let’s have a look how we can perform SHA-256 hashing operations using various Java libraries.

2. MessageDigest Class in Java

Java provides inbuilt MessageDigest class for SHA-256 hashing:

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] encodedhash = digest.digest(
  originalString.getBytes(StandardCharsets.UTF_8));

However, here we have to use a custom byte to hex converter to get the hashed value in hexadecimal:

private static String bytesToHex(byte[] hash) {
    StringBuffer hexString = new StringBuffer();
    for (int i = 0; i < hash.length; i++) {
    String hex = Integer.toHexString(0xff & hash[i]);
    if(hex.length() == 1) hexString.append('0');
        hexString.append(hex);
    }
    return hexString.toString();
}

3. Guava Library

The Google Guava library also provides a utility class for hashing.

First, let’s define the dependency:

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>20.0</version>
</dependency>

Now, here’s how we can use Guava to hash a String:

String sha256hex = Hashing.sha256()
  .hashString(originalString, StandardCharsets.UTF_8)
  .toString();

4. Apache Commons Codecs

Similarly, we can also use Apache Commons Codecs as well:

<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.10</version>
</dependency>

Here’s the utility class – called DigestUtils – that supports SHA-256 hashing:

String sha256hex = DigestUtils.sha256Hex(originalString);

5. Bouncy Castle Library

5.1. Maven Dependency

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk15on</artifactId>
    <version>1.55</version>
</dependency>

5.2. Hashing using the Bouncy Castle Library

The Bouncy Castle API provides a utility class for converting hex data to bytes and back again.

However, it is required to populate a digest using the built-in Java API first:

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(
  originalString.getBytes(StandardCharsets.UTF_8));
String sha256hex = new String(Hex.encode(hash));

6. Conclusion

In this quick article, we had a look at few ways of implementing SHA-256 hashing in Java, using both inbuilt and third party libraries.

The source code of the examples above can be found on the GitHub project.