bemurphy / krypter

Encrypts and signs a message.

krypter

Encrypts messages with authentication.

Usage

Pass a secret token. This must be at least 32 bytes long and should be really random. You can generate a random secret with SecureRandom.hex(32).

require "securerandom"
require "krypter"

secret = SecureRandom.hex(32)
encryptor = Krypter.new(secret)
encrypted = encryptor.encrypt("message")
encryptor.decrypt(encrypted) == "message"
# => true

# If the signature is invalid, it raises a `InvalidSignature` error.
encryptor.decrypt("")
# => Krypter::InvalidSignature

# If the message is changed, it raises a `InvalidMessage` error.
ciphertext, signature = encrypted.split("--")
ciphertext.reverse!

encryptor.decrypt([ciphertext, signature].join("--"))
# => Krypter::InvalidMessage

By default, the messages are encrypted with 256-bit AES in CBC mode (with random IV). The encrypted message is then signed with HMAC-SHA256, to prevent tampering and chosen ciphertext attacks.

The defaults can be changed when instantiating the encryptor object.

encryptor = Krypter.new(secret,
  cipher: "aes-256-cbc",
  digest: "SHA256",
  separator: "--"
)

Installation

$ gem install krypter