kryptos

A cryptography library for Gleam targeting both Erlang and JavaScript runtimes.

Why kryptos?

Runs on both Erlang and JavaScript (Node.js), wrapping each platform's native crypto APIs for consistent behavior.
All cryptographic operations delegate to the runtime's implementations (Erlang's crypto module, Node.js crypto module).
Inspired by Go's crypto library, the API guides you toward safe defaults and makes dangerous operations explicit.
Validated against Google's Wycheproof test vectors to catch edge-case vulnerabilities.

Note

Browser JavaScript is not supported. The WebCrypto API is promise-based, which doesn't fit the synchronous FFI model. For browser crypto, see plinth which provides Gleam bindings to WebCrypto using promises.

Installation

gleam add kryptos

Requirements

Erlang/OTP 27 or later for the Erlang target
Node.js 22 or later for the JavaScript target

Features

Module	Algorithms
aead	AES-GCM, AES-CCM, ChaCha20-Poly1305, XChaCha20-Poly1305
block	AES-128, AES-192, AES-256, AES Key Wrap (RFC 3394)
crypto	HKDF, PBKDF2, random bytes
ec	Key generation, import/export, introspection
ecdh	P-256, P-384, P-521, secp256k1
ecdsa	P-256, P-384, P-521, secp256k1
eddsa	Ed25519, Ed448
hash	SHA-1, SHA-2, SHA-3, SHAKE, BLAKE2
hmac	All hash algorithms
rsa	OAEP, PKCS#1 v1.5, PSS, PKCS#1 v1.5 signatures
x509/certificate	Certificate parsing and self-signed generation
x509/csr	CSR generation with ECDSA/RSA/EdDSA, SANs
xdh	X25519, X448

Getting Started

Encrypt and decrypt data using AES-GCM:

import kryptos/aead
import kryptos/block
import kryptos/crypto

pub fn main() {
  // Generate a random 256-bit key
  let assert Ok(cipher) = block.aes_256(crypto.random_bytes(32))
  let ctx = aead.gcm(cipher)

  // Generate a random nonce (never reuse with the same key!)
  let nonce = crypto.random_bytes(aead.nonce_size(ctx))

  // Encrypt
  let plaintext = <<"hello, world!":utf8>>
  let assert Ok(#(ciphertext, tag)) = aead.seal(ctx, nonce:, plaintext:)

  // Decrypt
  let assert Ok(decrypted) = aead.open(ctx, nonce:, ciphertext:, tag:)
  // decrypted == plaintext
}

Tip

If you're looking for a higher-level library for simple encryption, check out amaro.

Security

For guidance on choosing cryptographic primitives, see Cryptographic Right Answers.