FPE - Format Preserving Encryption Implementation in C

An implementation of the NIST approved FF1, FF3 and FF3-1 Format Preserving Encryption (FPE) algorithms in Python.

This package implements the FPE algorithm for Format Preserving Encryption as described in the March 2016 NIST publication 800-38G Methods for Format-Preserving Encryption, and revised on February 28th, 2019 with a draft update for FF3-1.

• NIST Recommendation SP 800-38G (FF3)
• NIST Recommendation SP 800-38G Revision 1 (FF3-1)
• NIST SP 800-38G Revision 1(2nd Public Draft)]

NOTE: NIST's Feburary 2025 Draft 2 has removed FF3 from the NIST standard. Contact me about a licensed version of FF1 in C.

Build and Run

To compile the example.c with the fpe library, just run

make

To build on macOS:

brew install openssl
export CFLAGS="-I$(brew --prefix openssl)/include"
export LDFLAGS="-L$(brew --prefix openssl)/lib"

Run the example in example.c.

./example EF4359D8D580AA4F7F036D6F04FC6A94 D8E7920AFA330A73 10 890121234567890000

plaintext: 890121234567890000

FF1 ciphertext: 318181603547192051
FF1 decrypted:  890121234567890000

FF3 ciphertext: 750918814058654607
FF3 decrypted:  890121234567890000

Testing

Run the tests

There are official test vectors for both FF1 and FF3 provided by NIST. You can run test.py with python 3.x. with a known test vector:

make test

Benchmarks

This library makes a simple set of benchmarks available.

make benchmark
./benchmark

Build Configuration

By default, this library uses 128-bit integers where supported for implementing the FF3 algorithm, and falls back to OpenSSL's bn library otherwise. This library makes macros available to customize or override this behavior for nonstandard compilers or certain use cases:

• FPE_USE_BIGNUM: always use bn for the FF3 algorithm.
• FPE_U128_TYPEDEF=<type>: define a typedef for an unsigned 128-bit integer to be used by the FF3 algorithm. If set, this will force 128-bit integer mode.

To pass in parameters, set the value of FPE_CFLAGS:

FPE_CFLAGS='-DFPE_USE_BIGNUM' make
FPE_CFLAGS='"-DFPE_U128_TYPEDEF=unsigned __int128"' make

Example Usage

This implementation is based on OpenSSL's BIGNUM and AES, so you need to install OpenSSL first.

There are several functions for FF1 and FF3 algorithm, respectively.

1. Create and delete FF1 key and tweak

FPE_KEY* FPE_ff1_create_key(const char *key, const char *tweak, const unsigned int radix);

void FPE_ff1_delete_key(FPE_KEY *keystruct);

name	description
key	encryption key (128 bit, 192 bits or 256 bits), represented as a c string
tweak	tweak, represented as a c string
radix	number of characters in the given alphabet, it must be in [2, 2^16]
returns	FPE_KEY structure

2. encrypt or decrypt text using FF1 algorithm

void FPE_ff1_encrypt(char *plaintext, char *ciphertext, FPE_KEY *keystruct)
void FPE_ff1_decrypt(char *ciphertext, char *plaintext, FPE_KEY *keystruct)

name	description
plaintext	numeral string to be encrypted, represented as an array of integers
ciphertext	encrypted numeral string, represented as an array of integers
keystruct	FPE_KEY structure that has been set with key and tweak

3. Create and delete FF3 key and tweak

FPE_KEY* FPE_ff3_create_key(const char *key, const char *tweak, const unsigned char radix);
FPE_KEY* FPE_ff3_1_create_key(const char *key, const char *tweak, const unsigned char radix);

void FPE_ff3_delete_key(FPE_KEY *keystruct);

name	description
key	encryption key (128 bit, 192 bits or 256 bits), represented as a c string
tweak	tweak, represented as a c string (it must be 64 bytes)
radix	number of characters in the given alphabet, it must be in [2, 62]
returns	FPE_KEY structure

4. encrypt or decrypt text using FF3 algorithm

void FPE_ff3_encrypt(char *plaintext, char *ciphertext, FPE_KEY *keystruct);
void FPE_ff3_decrypt(char *ciphertext, char *plaintext, FPE_KEY *keystruct);

name	description
plaintext	numeral string to be encrypted, represented as an array of integers
ciphertext	encrypted numeral string, represented as an array of integers
keystruct	FPE_KEY structure that has been set with key and tweak

TODO

1. Performance testing
2. Custom alphabet support