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crypto

Reference implementations of AES & SHA cryptographic functions in JavaScript.

These annotated implementations follow the standards very closely, in order to assist in studying the standards and underlying algorithms. Note for production use I would recommend the Web Cryptography API for the browser (see examples of SHA hashing, PBKDF2 key derivation, and AES-GCM encryption), or the crypto library in Node.js.

aes.js

This is a reference implementation of the AES (Rijndael cipher) algorithm described in the FIPS-197 standard.

This comprises:

  • cipher: takes a 128-bit input block and applies the cipher algorithm to produce a 128-bit output block
  • keyExpansion: applies a key expansion to a 128-/192-/256-bit cipher key to produce a 2D byte-array key schedule for the cipher routine

More details are available at www.movable-type.co.uk/scripts/aes.html; tests at www.movable-type.co.uk/scripts/test/aes-test.html.

aes-ctr.js

This is a counter-mode (CTR) wrapper for the AES function, following the method described in NIST SP 800-38A.

This comprises:

  • encrypt: encrypt a plaintext using a supplied password
  • decrypt: decrypt an encrypted ciphertext using a supplied password

These functions take and return (Unicode) strings. Internally they convert them (via UTF-8) to byte arrays for encryption as set out in NIST SP 800-38A.

Note that there are no standards for data storage formats of AES encryption mode wrapper functions, so this is unlikely to inter-operate with standard library functions.

More details are available at www.movable-type.co.uk/scripts/aes.html; tests at www.movable-type.co.uk/scripts/test/aes-test.html.

sha1.js

This is a reference implementation of the SHA-1 algorithm described in the FIPS-180-4 standard.

This comprises:

  • hash: takes a (Unicode) string and generates a hash (of the UTF-8 encoded string)

More details are available at www.movable-type.co.uk/scripts/sha1.html; tests at www.movable-type.co.uk/scripts/test/sha-test.html.

sha256.js

This is a reference implementation of the SHA-256 algorithm described in the FIPS-180-4 standard.

This comprises:

  • hash: takes a (Unicode) string and generates a hash (of the UTF-8 encoded string)

Note that while SHA-256 and SHA-512 are both members of the SHA-2 family, there is little common code, so they are in separate files here.

More details are available at www.movable-type.co.uk/scripts/sha256.html; tests at www.movable-type.co.uk/scripts/test/sha-test.html.

sha512.js

This is a reference implementation of the SHA-512 algorithm described in the FIPS-180-4 standard.

This comprises:

  • hash: takes a (Unicode) string and generates a hash (of the UTF-8 encoded string)

Note that while SHA-256 and SHA-512 are both members of the SHA-2 family, there is little common code, so they are in separate files here.

More details are available at www.movable-type.co.uk/scripts/sha512.html; tests at www.movable-type.co.uk/scripts/test/sha-test.html.

sha3.js

This is a reference implementation of the SHA-3 (Keccak) algorithm described in the FIPS-202 standard.

This comprises:

  • hash224: takes a (Unicode) string and generates a SHA3/224 hash (of the UTF-8 encoded string)
  • hash256: takes a (Unicode) string and generates a SHA3/256 hash (of the UTF-8 encoded string)
  • hash384: takes a (Unicode) string and generates a SHA3/384 hash (of the UTF-8 encoded string)
  • hash512: takes a (Unicode) string and generates a SHA3/512 hash (of the UTF-8 encoded string)

More details are available at www.movable-type.co.uk/scripts/sha3.html; tests at www.movable-type.co.uk/scripts/test/sha-test.html.

tea-block.js

Wheeler & Needham’s Tiny Encryption Algorithm is a simple but powerful encryption algorithm which provides strong encryption in just a few lines of concise, clear code. This implements the (corrected) ‘Block TEA’ variant (xxtea).

The library includes:

  • encrypt a text with a password
  • decrypt an encrypted text
  • encode an array of longs using a 128-bit key
  • decode an encoded array of longs

More details are available at www.movable-type.co.uk/scripts/tea-block.html; tests at www.movable-type.co.uk/scripts/test/tea-test.html.

Documentation

Documentation for all these methods is available at www.movable-type.co.uk/scripts/js/crypto/docs.

JavaScript

Cryptographically-speaking, browsers are inherently insecure (Node.js does not suffer the same problems), but these implementations are intended for study rather than production use. With its untyped C-style syntax, JavaScript reads remarkably close to pseudo-code: exposing the algorithms with a minimum of syntactic distractions.

These implementations are written in ES2015 version of JavaScript; ES2015 classes are both clearer and more familiar to users of other languages than the ES5 equivalents, and let and const are good practice and communicate intent better than var. Other idiomatic JavaScript which might be less familiar to users of other languages has generally been avoided.