Crypto.IDA

This module provides an (m,n)-information dispersal scheme that provides data redundancy while preserving secrecy. In other words, this module combines the best of 2 worlds: secret sharing algorithms with low-overhead information dispersal.

Function encode splits a given bytestring into n fragments with the following properties:

1. Any m of the n fragments are sufficient for reconstructing the original bytestring via decode, and
2. the knowledge of up to m-1 fragments does not leak any information about the original bytestring.

In more detail, suppose that we have some bytestring b that we want to (securely) disperse and parameter m, n. Running encode m n b does the following:

• Generate a randomly chosen key of 32 bytes, called key.
• Encrypt the bytestring b using key via AES.
• Generate n shares using the perfect secret sharing algorithm implemented in module Crypto.SecretSharing; see package http://hackage.haskell.org/package/secret-sharingsecret-sharing
• Generate n fragments of the encrypted data using the information dispersal algorithm in Data.IDA.
• Finally, we pair up these shares and fragments as a list of EncryptedFragments.

The size of each encrypted fragment is O(|b|/m + |key|). For sufficiently large bytestrings, the O(|b|/m) factor dominates and thus the scheme is space-optimal.

The secret sharing algorithm guarantess that the knowledge of up to m-1 of the fragments does not leak any information about the encryption key (and hence the encrypted data).

Documentation

data EncryptedFragment

Instances

Eq EncryptedFragment

Show EncryptedFragment

Generic EncryptedFragment

Binary EncryptedFragment

Typeable * EncryptedFragment

type Rep EncryptedFragment

encode

Arguments

:: Int

m: number of fragments required for reconstruction

-> Int

n: total number of fragments (n ≥ m)

-> ByteString

the information that we want to disperse

-> IO [EncryptedFragment]

a list of n encrypted fragments.

Space efficient and secrecy-preserving (m,n)-information dispersal: Generates n fragments out of a given bytestring b. Each fragment has size length b / m + O(1). At least m fragments are required for reconstruction. Preserves secrecy: The knowledge of less than m fragments provides no information about the original data whatsoever.

encodeWithIV

Arguments

:: Int

m: number of fragments required for reconstruction

-> Int

n: total number of fragments (n ≥ m)

-> ByteString

the initialization vector for the AES encryption

-> ByteString

the information that we want to disperse

-> IO [EncryptedFragment]

a list of n encrypted fragments.

Same as encode but uses an initialization vector for the AES encryption.

decode :: [EncryptedFragment] -> ByteString

Reconstruct the original data from (at least) m fragments. Throws an AssertionFailed exception if an insufficient number fragments are given or if a decoding error occurs.