An efficient public key cryptography library for Ruby providing key exchange/agreement.
This gem implements X25519 (a.k.a. Curve25519) Elliptic Curve Diffie-Hellman function as described in RFC7748 as a C extension using the high performance rfc7748_precomputed implementation based on the paper How to (pre-)compute a ladder (with fallback to the ref10 C implementation).
X25519 is one of two notable algorithms implemented atop the Curve25519 elliptic curve. The ed25519 gem is a related project of this one, and implements the Ed25519 signature scheme on the twisted Edwards form of Curve25519.
X25519 is a key exchange/agreement algorithm generally used as a low-level building block in cryptographic protocols.
Please use RbNaCl::Box if you would like a high-level construction which uses X25519 for public-key encryption. Otherwise, the X25519 algorithm is not directly useful for encryption without a higher-level encryption protocol built on top of it.
x25519.rb is supported on and tested against the following platforms:
- MRI 2.5, 2.6, 2.7, 3.0
Add this line to your application's Gemfile:
gem "x25519"And then execute:
$ bundle
Or install it yourself as:
$ gem install x25519
The example below shows how to perform a full Diffie-Hellman key exchange:
require "x25519"
# Alice generates random scalar (private key)
alice_sk = X25519::Scalar.generate
# Alice obtains public key for her private key/scalar
alice_pk = alice_sk.public_key
# Bob generates random scalar (private key)
# Ostensibly this would be on a different computer somewhere
bob_sk = X25519::Scalar.generate
bob_pk = bob_sk.public_key
# Alice can perform Diffie-Hellman with Bob's public key
alice_secret = alice_sk.diffie_hellman(bob_pk).to_bytes
# Bob can perform Diffie-Hellman with Alice's public key
bob_secret = bob_sk.diffie_hellman(alice_pk).to_bytes
# The resulting secrets should be the same
alice_secret == bob_secret # trueThe X25519::Scalar class represents secret integers used as X25519 private
keys. These secret integers are multiplied by a well-known base point to
obtain X25519 public keys (X25519::MontgomeryU).
Generate a random private scalar (using SecureRandom)
Example:
secret_key = X25519::Scalar.generatebytes: a 32-byteStringvalue containing the private key
Example:
secret_key = X25519::Scalar.new(File.read("alice.key"))NOTE: The #multiply_base method is an alias of this one.
Performs fixed-base scalar multiplication (i.e. calculates public key)
Return Value:
Returns a X25519::MontgomeryU object which represents the public key for this private key/scalar.
Example:
secret_key = X25519::Scalar.generate
public_key = secret_key.public_keyNOTE: The #multiply method is an alias of this one.
Performs variable-base scalar multiplication, computing a shared secret between our private scalar and someone else's public key/point.
Arguments:
other_public_key: aX25519::MontgomeryUobject containing the public key with which we'd like to compute a shared secret.
Return Value:
Returns a X25519::MontgomeryU object which represents the shared secret.
Example:
secret_key = X25519::Scalar.generate
public_key = X25519::MontgomeryU.new(File.read("bob.pub"))
# Returns an X25519::MontgomeryU
shared_secret = secret_key.multiply(public_key)
# Obtain the shared secret as a serialized byte representation
shared_secret_bytes = shared_secret.to_bytesReturn Value:
Returns a String containing a byte representation of this scalar:
Example:
secret_key = X25519::Scalar.new(...)
File.write("alice.key", secret_key.to_bytes)The X25519::MontgomeryU class represents a coordinate (specifically a
Montgomery-u coordinate) on the elliptic curve. In the X25519 Diffie-Hellman
function, these serve both as public keys and as shared secrets.
Arguments:
bytes: a 32-byteStringvalue containing the public key
Example:
public_key = X25519::MontgomeryU.new(File.read("bob.pub"))Return Value:
Returns a String containing a byte representation of a compressed Montgomery-u coordinate:
Example:
public_key = X25519::MontgomeryU..new(...)
File.write("bob.pub", public_key.to_bytes)If you'd like to avoid the object-oriented API, you can use a simplified API which acts entirely on bytestrings.
Arguments:
secret_key: a 32-byteStringcontaining a private scalarpublic_key: a 32-byteStringcontaining a compressed Montgomery-u coordinate
Return Value:
Returns a String containing a 32-byte compressed Montgomery-u coordinate
Bug reports and pull requests are welcome on GitHub at https://github.com/RubyCrypto/x25519. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.
This gem contains two implementations of X25519: an optimized assembly implementation and a portable C implementation. Implementations are selected based on available CPU features.
rfc7748_precomputed: optimized assembly implementation
- Prime field arithmetic is optimized for the 4th and 6th generation of Intel Core processors (Haswell and Skylake micro-architectures).
- Efficient integer multiplication using MULX instruction.
- Integer additions accelerated with ADCX/ADOX instructions.
- Key generation uses a read-only table of 8 KB for X25519.
- Taken from the SUPERCOP cryptographic benchmarking suite (supercop-20171020)
- Portable C code which should compile on any architecture
The X25519 Diffie-Hellman function was originally designed by Dan Bernstein:
The optimized rfc7748_precomputed implementation was designed by:
- Thomaz Oliveira, Computer Science Department, Cinvestav-IPN, Mexico.
- Julio López, University of Campinas, Brazil.
- Hüseyin Hisil, Yasar University, Turkey.
- Armando Faz-Hernández, University of Campinas, Brazil.
- Francisco Rodríguez-Henríquez, Computer Science Department, Cinvestav-IPN, Mexico.
Copyright (c) 2017-2018 Armando Faz Copyright (c) 2017-2021 Tony Arcieri
This gem is available as open source under the terms of the BSD-3 Clause License (LICENSE)
Everyone interacting in the x25519.rb project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.