Time-Based One-Time Password (RFC 6238) and HMAC-Based One-Time Password (RFC 4226) reference implementations and more.

// Passwords will be 6 digits, change every 30 seconds, and are computed with SHA-1.
TOTP totp = new TOTP(6, Duration.ofSeconds(30L), Keys.generate("HmacSHA1", 160), SHA1.getInstance());

totp.compute(Instant.now());
// OR
totp.compute(Instant.now().toEpochMillis());

// Passwords will be 6 digits and are computed with SHA-1.
HOTP hotp = new HOTP(6, Keys.generate("HmacSHA1", 160), SHA1.getInstance());

hotp.compute(0L);

byte[] input = "Hello, World!".getBytes();

// Create an HMAC instance.
HMAC hmac = new HMAC(Keys.generate("AES"), SHA1.getInstance());

// Sign the input.
byte[] tag = hmac.sign(input);

...

// Verify the input later.
boolean valid = hmac.verify(input, tag);

Alternatively, you can use JceMAC, which wraps JCE's Mac:

JceMac hmac = new JceMac(Keys.generate("AES"), "HmacSHA1");

Classes: MD2, MD5, SHA1, SHA224, SHA256, SHA384, SHA512, SHA512t224, SHA512t256.

byte[] input = "Hello, World!".getBytes();

// Hash the input using SHA-1.
byte[] hash = SHA1.getInstance().compute(input);

Keys:

• byte[] generate(String algorithm, SecureRandom secureRandom) – Generates a key, specifying the algorithm and SecureRandom.
• byte[] generate(String algorithm, int keySize) – Generates a key, specifying the algorithm and key size in bytes.
• byte[] generate(String algorithm) – Generates a key, specifying the algorithm.

Bytes:

• byte[] concatenate(byte[] array, byte[]... arrays) – Concatenates n-arrays.
• byte[] xor(byte[] array1, byte[] array2) – XOR operation on two arrays.
• byte[] toHex(byte[] bytes) – Converts bytes to hexadecimal bytes.

This code is under the BSD 3-Clause.

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