CIRCL

CIRCL (Cloudflare Interoperable, Reusable Cryptographic Library) is a collection of cryptographic primitives written in Go. The goal of this library is to be used as a tool for experimental deployment of cryptographic algorithms targeting Post-Quantum (PQ) and Elliptic Curve Cryptography (ECC).

Security Disclaimer

🚨 This library is offered as-is, and without a guarantee. Therefore, it is expected that changes in the code, repository, and API occur in the future. We recommend to take caution before using this library in a production application since part of its content is experimental. All security issues must be reported, please notify us immediately following the instructions given in our Security Policy.

Constant-Time Caveats

⚠️ Not every package in CIRCL is constant time. The following packages document, at the top of their doc.go or main source file, the specific operations that are known to leak timing information: group/, oprf/, blindsign/blindrsa/partiallyblindrsa/, secretsharing/, tss/rsa/, zk/dl/, zk/dleq/, and ecc/p384/.

Installation

You can get CIRCL by fetching:

go get -u github.com/cloudflare/circl

Alternatively, look at the Cloudflare Go fork to see how to integrate CIRCL natively in Go.

List of Algorithms

Elliptic Curve Cryptography

• X25519 and X448 functions. (RFC-7748)
• Curve4Q function based on FourQ curve. (draft-ladd-cfrg-4q)

• Ed25519 and Ed448 signatures. (RFC-8032)
• BLS signatures. (draft-irtf-cfrg-bls-signature)

• P-256, P-384, P-521. (FIPS 186-5)
• Ristretto group. (RFC-9496)
• Bilinear pairings: with the BLS12-381 curve, and hash to G1 and G2.
• Hash to curve, hash to field, XMD and XOF expanders. (RFC-9380)

• HPKE: Hybrid Public-Key Encryption (RFC-9180)
• VOPRF: Verifiable Oblivious Pseudorandom functions. (RFC-9497)
• RSA Blind Signatures. (RFC-9474)
• Partially-blind RSA Signatures. (draft-cfrg-partially-blind-rsa)
• CPABE: Ciphertext-Policy Attribute-Based Encryption. (ia.cr/2019/966)
• OT: Simplest Oblivious Transfer (ia.cr/2015/267).
• Threshold RSA Signatures (Shoup Eurocrypt 2000).
• Prio3 Verifiable Distributed Aggregation Function (draft-irtf-cfrg-vdaf).

Post-Quantum Cryptography

• ML-KEM: modes 512, 768, 1024 (FIPS-203).
• X-Wing (draft-connolly-cfrg-xwing-kem).
• Kyber KEM: modes 512, 768, 1024 (KYBER).
• FrodoKEM: modes 640-SHAKE. (FrodoKEM)
• CSIDH: Post-Quantum Commutative Group Action (CSIDH).
• (insecure, deprecated) SIDH/SIKE: Supersingular Key Encapsulation with primes p434, p503, p751 (SIKE).

• Dilithium: modes 2, 3, 5 (Dilithium).
• ML-DSA: modes 44, 65, 87 (FIPS 204).
• SLH-DSA: twelve parameter sets, pure and pre-hash signing (FIPS 205).

Zero-knowledge Proofs

• Schnorr: Prove knowledge of the Discrete Logarithm. (RFC-8235)
• DLEQ: Prove knowledge of the Discrete Logarithm Equality. (RFC-9497)
• DLEQ in Qn: Prove knowledge of the Discrete Logarithm Equality for subgroup of squares in (Z/nZ)*.

Symmetric Cryptography

• SHAKE128 and SHAKE256 (FIPS 202).
• BLAKE2X: BLAKE2XB and BLAKE2XS (Blake2x)
• KangarooTwelve: fast hashing based on Keccak-p. (KangarooTwelve).
• SIMD Keccak f1600 Permutation.

• Ascon v1.2: Family of AEAD block ciphers (ASCON)

Misc

• Safe primes generation.
• Integer encoding: wNAF, regular signed digit, mLSBSet representations.

• Fp25519, Fp448, Fp511, Fp434, Fp503, Fp751.
• Fp381, and its quadratic, sextic and twelveth extensions.
• Polynomials in monomial and Lagrange basis.

• P-384 Curve
• FourQ
• Goldilocks
• BLS12-381

Testing and Benchmarking

Library comes with number of make targets which can be used for testing and benchmarking:

• test performs testing of the binary.
• bench runs benchmarks.
• cover produces coverage.
• lint runs set of linters on the code base.

Contributing

To contribute, fork this repository and make your changes, and then make a Pull Request. A Pull Request requires approval of the admin team and a successful CI build.

How to Cite

To cite CIRCL, use one of the following formats and update the version and date you accessed this project.

APA Style

Faz-Hernandez, A. and Kwiatkowski, K. (2019). Introducing CIRCL:
An Advanced Cryptographic Library. Cloudflare. Available at
https://github.com/cloudflare/circl. v1.6.4 Accessed Jun, 2026.

BibTeX Source

@manual{circl,
  title        = {Introducing CIRCL: An Advanced Cryptographic Library},
  author       = {Armando Faz-Hernandez and Kris Kwiatkowski},
  organization = {Cloudflare},
  abstract     = {{CIRCL (Cloudflare Interoperable, Reusable Cryptographic Library) is
                   a collection of cryptographic primitives written in Go. The goal
                   of this library is to be used as a tool for experimental
                   deployment of cryptographic algorithms targeting Post-Quantum (PQ)
                   and Elliptic Curve Cryptography (ECC).}},
  note         = {Available at \url{https://github.com/cloudflare/circl}. v1.6.4 Accessed Jun, 2026},
  month        = jun,
  year         = {2019}
}

CFF Style

See attached CITATION.cff file.

License

The project is licensed under the BSD-3-Clause License.