Crypto.Saltine.Core.Stream

Secret-key encryption: Crypto.Saltine.Core.Stream

The stream function produces a sized stream ByteString as a function of a secret key and a nonce. The xor function encrypts a message ByteString using a secret key and a nonce. The xor function guarantees that the ciphertext has the same length as the plaintext, and is the plaintext xor stream k n. Consequently xor can also be used to decrypt.

The stream function, viewed as a function of the nonce for a uniform random key, is designed to meet the standard notion of unpredictability ("PRF"). For a formal definition see, e.g., Section 2.3 of Bellare, Kilian, and Rogaway, "The security of the cipher block chaining message authentication code," Journal of Computer and System Sciences 61 (2000), 362–399; http://www-cse.ucsd.edu/~mihir/papers/cbc.html. This means that an attacker cannot distinguish this function from a uniform random function. Consequently, if a series of messages is encrypted by xor with a different nonce for each message, the ciphertexts are indistinguishable from uniform random strings of the same length.

Note that the length is not hidden. Note also that it is the caller's responsibility to ensure the uniqueness of nonces—for example, by using nonce 1 for the first message, nonce 2 for the second message, etc. Nonces are long enough that randomly generated nonces have negligible risk of collision.

Saltine does not make any promises regarding the resistance of crypto_stream to "related-key attacks." It is the caller's responsibility to use proper key-derivation functions.

Crypto.Saltine.Core.Stream is crypto_stream_xsalsa20, a particular cipher specified in "Cryptography in NaCl" (http://nacl.cr.yp.to/valid.html), Section 7. This cipher is conjectured to meet the standard notion of unpredictability.

This is version 2010.08.30 of the stream.html web page.

Documentation

data Key

An opaque stream cryptographic key.

Instances

Eq Key

Methods

(==) :: Key -> Key -> Bool

(/=) :: Key -> Key -> Bool

Ord Key

Methods

compare :: Key -> Key -> Ordering

(<) :: Key -> Key -> Bool

(<=) :: Key -> Key -> Bool

(>) :: Key -> Key -> Bool

(>=) :: Key -> Key -> Bool

max :: Key -> Key -> Key

min :: Key -> Key -> Key

IsEncoding Key

Methods

encode :: Key -> ByteString

decode :: ByteString -> Maybe Key

encoded :: (Choice p, Applicative f) => p Key (f Key) -> p ByteString (f ByteString)

data Nonce

An opaque stream nonce.

Instances

Eq Nonce

Methods

(==) :: Nonce -> Nonce -> Bool

(/=) :: Nonce -> Nonce -> Bool

Ord Nonce

Methods

compare :: Nonce -> Nonce -> Ordering

(<) :: Nonce -> Nonce -> Bool

(<=) :: Nonce -> Nonce -> Bool

(>) :: Nonce -> Nonce -> Bool

(>=) :: Nonce -> Nonce -> Bool

max :: Nonce -> Nonce -> Nonce

min :: Nonce -> Nonce -> Nonce

IsNonce Nonce

Methods

zero :: Nonce

nudge :: Nonce -> Nonce

IsEncoding Nonce

Methods

encode :: Nonce -> ByteString

decode :: ByteString -> Maybe Nonce

encoded :: (Choice p, Applicative f) => p Nonce (f Nonce) -> p ByteString (f ByteString)

newKey :: IO Key

Creates a random key of the correct size for stream and xor.

newNonce :: IO Nonce

Creates a random nonce of the correct size for stream and xor.

stream

Arguments

:: Key

-> Nonce

-> Int

-> ByteString

Cryptographic stream

Generates a cryptographic random stream indexed by the Key and Nonce. These streams are indistinguishable from random noise so long as the Nonce is not used more than once.

xor

Arguments

:: Key

-> Nonce

-> ByteString

Message

-> ByteString

Ciphertext

Computes the exclusive-or between a message and a cryptographic random stream indexed by the Key and the Nonce. This renders the output indistinguishable from random noise so long as the Nonce is not used more than once. Note: while this can be used for encryption and decryption, it is possible for an attacker to manipulate the message in transit without detection. USE AT YOUR OWN RISK.