Correct bug in BPS encryption algorithm #21
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There is a typo in the algorithm 3 (the encryption algorithm) in [1].
This has the consequence that when the plaintext length is longer than maxb (i.e. when you use the Mode of Operation described in the section 1.2 of [1]) and the plaintext length is a multiple of maxb, FPE_decrypt(FPE_encrypt(X)) != X.
You can test this case easily by changing the line 314 of mrfpe.c to n=112.
In this case, the radix s is 10 which mean maxb(s) = 56.
You can see that the plaintext obtained by decrypting the ciphertext is not equal to the original plaintext.
[1] BPS: a Format-Preserving Encryption Proposal, Eric Brier, Thomas Peyrin and Jacques Stern,
http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/bps/bps-spec.pdf