SpeckEx.CTR (SpeckEx v0.1.0)

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Counter (CTR) mode encryption using the Speck block cipher.

This module provides stream cipher encryption using Speck in CTR mode, allowing encryption of data of arbitrary length. CTR mode turns a block cipher into a stream cipher by encrypting a counter value.

Here be dragons

This is a "no guardrails" implementation module, where nonce generation is your own responsibility. Use the main SpeckEx module unless you know what you are doing. Be sure to read the SpeckEx security guidelines.

Supported Variants

Only Speck variants with 32, 64 and 128-bit block sizes are supported because of limitations of the backing Rust "ctr" crate:

  • :speck32_64 - 32-bit block, 64-bit key (4-byte block, 8-byte key)
  • :speck64_96 - 64-bit block, 96-bit key (8-byte block, 12-byte key)
  • :speck64_128 - 64-bit block, 128-bit key (8-byte block, 16-byte key)
  • :speck128_128 - 128-bit block, 128-bit key (16-byte block, 16-byte key)
  • :speck128_192 - 128-bit block, 192-bit key (16-byte block, 24-byte key)
  • :speck128_256 - 128-bit block, 256-bit key (16-byte block, 32-byte key, default)

Usage

# Generate a random key (32 bytes for default speck128_256)
iex> key = :crypto.strong_rand_bytes(32)
iex> nonce = :crypto.strong_rand_bytes(16)
iex> ciphertext = SpeckEx.CTR.crypt("Secret message", key, nonce)
iex> SpeckEx.CTR.crypt(ciphertext, key, nonce)
"Secret message"

Summary

Types

variant()

Speck variants with 32, 64 and 128-bit block sizes, supported by CTR and AEAD modes.

Functions

crypt(data, key, nonce, variant \\ :speck128_256)

En/decrypt using CTR mode.

Types

variant()

@type variant() ::
  :speck32_64
  | :speck64_96
  | :speck64_128
  | :speck128_128
  | :speck128_192
  | :speck128_256

Speck variants with 32, 64 and 128-bit block sizes, supported by CTR and AEAD modes.

Functions

crypt(data, key, nonce, variant \\ :speck128_256)

@spec crypt(binary(), binary(), binary(), variant()) :: binary()

En/decrypt using CTR mode.

Parameters

  • data - The data to en/decrypt (binary, any length)
  • key - The encryption key (size depends on variant)
  • nonce - The initialization vector (size depends on variant, MUST be unique per key)
  • variant - The Speck variant to use (default: :speck128_256)

Returns

The encrypted ciphertext or decrypted plaintext as a binary (same length as data).

Examples

iex> key = :crypto.strong_rand_bytes(32)
iex> nonce = :crypto.strong_rand_bytes(16)
iex> ciphertext = SpeckEx.CTR.crypt("Hello, World!", key, nonce)
iex> is_binary(ciphertext) and byte_size(ciphertext) == byte_size("Hello, World!")
true