Raaz.Cipher.Internal

This module exposes the low-level internal details of ciphers. Do not import this module unless you want to implement a new cipher or give a new implementation of an existing cipher.

Internals of a cipher.

Ciphers provide symmetric encryption in the raaz library and are captured by the type class Cipher. They are instances of the class Symmetric and the associated type Key captures the all that is required to determine the encryption and decryption process. In most ciphers, this includes what is know as the _encryption key_ as well as the _initialisation vector_.

Instances of Cipher is only required to provide full block encryption/decryption algorithms. Implementations are captured by two types.

CipherI:

Values of this type that captures implementations of a cipher. This type is parameterised over the memory element that is used internally by the implementation.

SomeCipherI:

The existentially quantified version of CipherI over its memory element. By wrapping the memory element inside the existential quantifier, values of this type exposes only the interface and not the internals of the implementation. The Implementation associated type of a cipher is the type SomeCipherI

To support a new cipher, a developer needs to:

1. Define a new type which captures the cipher. This type should be an instance of the class Cipher.
2. Define an implementation, i.e. a value of the type SomeCipherI.
3. Define a recommended implementation, i.e. an instance of the type class Recommendation

class (Primitive cipher, Implementation cipher ~ SomeCipherI cipher, Describable cipher) => Cipher cipher

Class capturing ciphers. The implementation of this class should give an encryption and decryption algorithm for messages of length which is a multiple of the block size. Needless to say, the encryption and decryption should be inverses of each other for such messages.

Instances

Cipher ChaCha20

Defined in Raaz.Cipher.ChaCha20.Internal

Cipher (AES 128 CBC)

Defined in Raaz.Cipher.AES.Internal

Cipher (AES 192 CBC)

Defined in Raaz.Cipher.AES.Internal

Cipher (AES 256 CBC)

Defined in Raaz.Cipher.AES.Internal

data CipherMode

Block cipher modes.

Constructors

CBC

Cipher-block chaining

CTR

Counter

Instances

Eq CipherMode

Defined in Raaz.Cipher.Internal

Methods

(==) :: CipherMode -> CipherMode -> Bool

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

Show CipherMode

Defined in Raaz.Cipher.Internal

Methods

showsPrec :: Int -> CipherMode -> ShowS

show :: CipherMode -> String

showList :: [CipherMode] -> ShowS

Cipher implementation

data CipherI cipher encMem decMem

The implementation of a block cipher.

Constructors

CipherI

Fields

• cipherIName :: String
• cipherIDescription :: String
• encryptBlocks :: Pointer -> BLOCKS cipher -> MT encMem ()

  The underlying block encryption function.

• decryptBlocks :: Pointer -> BLOCKS cipher -> MT decMem ()

  The underlying block decryption function.

• cipherStartAlignment :: Alignment

Instances

Describable (CipherI cipher encMem decMem)

Defined in Raaz.Cipher.Internal

Methods

name :: CipherI cipher encMem decMem -> String

description :: CipherI cipher encMem decMem -> String

BlockAlgorithm (CipherI cipher encMem decMem)

Defined in Raaz.Cipher.Internal

Methods

bufferStartAlignment :: CipherI cipher encMem decMem -> Alignment

data SomeCipherI cipher

Some implementation of a block cipher. This type is existentially quantifies over the memory used in the implementation.

Constructors

CipherM cipher encMem decMem => SomeCipherI (CipherI cipher encMem decMem)

Instances

Describable (SomeCipherI cipher)

Defined in Raaz.Cipher.Internal

Methods

name :: SomeCipherI cipher -> String

description :: SomeCipherI cipher -> String

BlockAlgorithm (SomeCipherI cipher)

Defined in Raaz.Cipher.Internal

Methods

bufferStartAlignment :: SomeCipherI cipher -> Alignment

Stream ciphers.

Stream ciphers are special class of ciphers which can encrypt messages of any length (not necessarily multiples of block length). Typically, stream ciphers are obtained by xoring the data with a stream of prg values that the stream ciphers generate. As a consequence, the encryption and decryption is the same algorithm. one can also use the stream cipher as a pseudo-random generator.

We have the class StreamCipher that captures valid stream ciphers.

class Cipher cipher => StreamCipher cipher

Class that captures stream ciphers. An instance of StreamCipher should be an instance of Cipher, with the following additional constraints.

1. The encryption and decryption should be the same algorithm.
2. Encryption/decryption can be applied to a messages of length l even if l is not a multiple of block length.
3. The encryption of a prefix of a length l of a message m should be the same as the l length prefix of the encryption of m.

It is the duty of the implementer of the cipher to ensure that the above conditions are true before declaring an instance of a stream cipher.

Instances

StreamCipher ChaCha20

Defined in Raaz.Cipher.ChaCha20.Internal

makeCipherI

Arguments

:: String

name

-> String

description

-> (Pointer -> BLOCKS prim -> MT mem ())

stream transformer

-> Alignment

buffer starting alignment

-> CipherI prim mem mem

Constructs a CipherI value out of a stream transformation function. Useful in building a Cipher instance of a stream cipher.

transform :: (StreamCipher c, Recommendation c) => c -> Key c -> ByteString -> ByteString

Transform a given bytestring using the recommended implementation of a stream cipher.

transform' :: StreamCipher c => c -> Implementation c -> Key c -> ByteString -> ByteString

Transforms a given bytestring using a stream cipher. We use the transform instead of encrypt/decrypt because for stream ciphers these operations are same.

Unsafe encryption and decryption.

We expose some unsafe functions to encrypt and decrypt bytestrings. These function works correctly only if the input byte string has a length which is a multiple of the block size of the cipher and hence are unsafe to use as general methods of encryption and decryption of data. Use these functions for testing and benchmarking and nothing else.

There are multiple ways to handle arbitrary sized strings like padding, cipher block stealing etc. They are not exposed here though.

unsafeEncrypt

Arguments

:: (Cipher c, Recommendation c)

=> c

The cipher

-> Key c

The key to use

-> ByteString

The string to encrypt

-> ByteString

Encrypt using the recommended implementation. This function is unsafe because it only works correctly when the input ByteString is of length which is a multiple of the block length of the cipher.

unsafeDecrypt

Arguments

:: (Cipher c, Recommendation c)

=> c

The cipher

-> Key c

The key to use

-> ByteString

The string to encrypt

-> ByteString

Decrypt using the recommended implementation. This function is unsafe because it only works correctly when the input ByteString is of length which is a multiple of the block length of the cipher.

unsafeEncrypt'

Arguments

:: Cipher c

=> c

The cipher to use

-> Implementation c

The implementation to use

-> Key c

The key to use

-> ByteString

The string to encrypt.

-> ByteString

Encrypt the given ByteString. This function is unsafe because it only works correctly when the input ByteString is of length which is a multiple of the block length of the cipher.

unsafeDecrypt'

Arguments

:: Cipher c

=> c

The cipher to use

-> Implementation c

The implementation to use

-> Key c

The key to use

-> ByteString

The string to encrypt.

-> ByteString

Decrypts the given ByteString. This function is unsafe because it only works correctly when the input ByteString is of length which is a multiple of the block length of the cipher.