fastfpe

Fast Format Preserving Encryption (FPE) implementation in Rust with Python bindings.

Format-preserving encryption (FPE) is a cryptographic method that encrypts data while preserving its format. For example, encrypting a credit card number yields another valid-looking credit card number, making it useful for data protection while maintaining compatibility with existing systems.

Features

• FF1 and FF3-1 Format Preserving Encryption algorithms
• Fast Rust implementation with Python bindings
• Support for custom alphabets
• Thread-safe

[!Note]: As of late 2025, FF3/FF3-1 are no longer recommended in some security guidance due to design concerns. FF1 is fully supported here and recommended for new deployments. FF3-1 remains available for compatibility and migration.

Installation

pip install fastfpe

Usage (FF3-1)

>>> from fastfpe import ff3_1
>>>
>>> key = "3eaa133d22a7ee2432fb8ecfde1e97d9106dcf26b9edaa52b3ed4acd9a9b8445"
>>> tweak = "5be49f26c1dbb7"  # 7 bytes (14 hex chars)
>>> alphabet = "abcdef0123456789"
>>> plaintext = "024587931578"
>>>
>>> ciphertext = ff3_1.encrypt(key, tweak, alphabet, plaintext)
>>> ciphertext
'd756b8704a2d'
>>> ff3_1.decrypt(key, tweak, alphabet, ciphertext)
'024587931578'

Usage (FF1)

>>> from fastfpe import ff1
>>>
>>> # 128/192/256-bit AES keys supported (16/24/32 bytes -> 32/48/64 hex chars)
>>> key = "2b7e151628aed2a6abf7158809cf4f3c"  # 128-bit key
>>> tweak = ""  # FF1 tweak may be empty or longer (length impacts security domain sizing)
>>> alphabet = "0123456789"
>>> plaintext = "0123456789"
>>>
>>> ciphertext = ff1.encrypt(key, tweak, alphabet, plaintext)
>>> ciphertext
'2433477484'
>>> ff1.decrypt(key, tweak, alphabet, ciphertext)
'0123456789'

Notes:

• FF1 tweak can be empty; size limits depend on NIST SP 800-38G constraints (radix and length bounds enforced internally).
• Provide a non-empty tweak for domain separation across contexts.
• Both algorithms return ValueError with descriptive messages on invalid inputs.

Performance

As expected, fastfpe is much faster than the reference python implementation. The gains are more pronounced with larger plaintexts.

The following benchmarks were performed on an Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz.

Running 10,000 iterations, 5 times each, 12-byte plaintext
--------------------------------------------------

Python implementation: 0.110 ms/op (± 0.001 ms)
Rust implementation:   0.008 ms/op (± 0.000 ms)
Rust is 13.2x faster

Running 10,000 iterations, 5 times each, 16-byte plaintext
--------------------------------------------------

Python implementation: 0.133 ms/op (± 0.002 ms)
Rust implementation:   0.009 ms/op (± 0.000 ms)
Rust is 14.5x faster

Running 10,000 iterations, 5 times each, 20-byte plaintext
--------------------------------------------------

Python implementation: 0.161 ms/op (± 0.005 ms)
Rust implementation:   0.010 ms/op (± 0.002 ms)
Rust is 15.9x faster

Running 10,000 iterations, 5 times each, 24-byte plaintext
--------------------------------------------------

Python implementation: 0.189 ms/op (± 0.004 ms)
Rust implementation:   0.011 ms/op (± 0.000 ms)
Rust is 16.8x faster

Support Matrix

If you need other targets (e.g., musllinux, ppc64le) open an issue or PR.

License

Licensed under the MIT License. See LICENSE for more information.

Uses the rust-fpe implementation by johntyner, under the MIT License.

Uses the ff3 python package by mysto as a reference implementation, under the Apache 2.0 License.