Spritz in Emacs

Spritz is a stream cipher by Ron Rivest and Jacob Schuldt. It's essentially a redesign of RC4 using modern cryptographics tools and knowledge. This implementation is based directly on the whitepaper, implementing the the exact set of low-level primitives.

Notice: Spritz was broken in 2016 and should not be used for security purposes.

Spritz is a "sponge function" and, as such, has an API analgous to a sponge. It absorbs bytes and is squeezed to emit bytes. This is the sponge API:

• spritz-create -- initializes a new state
• spritz-copy -- copy an existing state
• spritz-absorb -- absorb bytes into the state
• spritz-absorb-stop -- cleanly separates different inputs
• spritz-drip -- output a single byte
• spritz-squeeze -- output multiple bytes (convenience)

These methods are used to implement all sorts of cryptographic functions: hash, MAC, PRNG, encryption, and decryption. Some of these are provided as a slightly highter level API:

• spritz-hash -- hashes a string or a buffer
• spritz-random -- random number generator (like cl-random)
• spritz-random-iv -- generate a secure initialization vector (IV)
• spritz-random-uuid -- generate a version 4 UUID

The "random" functions will, by default, use an internal random state that is seeded at package load time by a dozen different sources of entropy. This ensures the output of the PRNG functions is secure. Additional entropy, such as bytes from /dev/random, can be absorbed into this state by passing it to `spritz-random-stir'. Accidentally absorbing non-random data is harmless.

Finally, two user interface commands are defined. These use Spritz as both a stream cipher and key derivation function.

• spritz-encrypt-buffer
• spritz-decrypt-buffer

Test vectors can be found in the unit tests.