rustls-ccm

AES-CCM cipher suites for rustls.

Neither aws-lc-rs nor ring expose AES-CCM, so rustls's built-in providers cannot offer these suites. This crate fills the gap using the RustCrypto aes + ccm crates, plugged in via rustls's CryptoProvider extension point.

Why

CCM cipher suites are required or recommended by several IoT and energy protocols:

• IEEE 2030.5 (Smart Energy) — mandates TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
• Matter / Thread — uses TLS 1.3 TLS_AES_128_CCM_SHA256
• RFC 7925 (constrained-device TLS) — profiles CCM and CCM-8 suites
• CoAP over DTLS — commonly uses CCM-8 for bandwidth efficiency

Without this crate, using rustls for these protocols requires falling back to OpenSSL or BoringSSL (which removed CCM entirely).

Cipher suites

TLS 1.2 (RFC 7251)

Suite	Tag	Key
TLS_ECDHE_ECDSA_WITH_AES_128_CCM	16 B	128-bit
TLS_ECDHE_ECDSA_WITH_AES_256_CCM	16 B	256-bit
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8	8 B	128-bit
TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8	8 B	256-bit

TLS 1.3 (RFC 8446)

Suite	Tag	Key
TLS_AES_128_CCM_SHA256	16 B	128-bit
TLS_AES_128_CCM_8_SHA256	8 B	128-bit

Usage

[dependencies]
rustls-ccm = "0.1"
rustls = "0.23"

Quick start — all CCM suites

let provider = rustls_ccm::crypto_provider();
let config = rustls::ClientConfig::builder_with_provider(provider.into())
    .with_safe_default_protocol_versions()
    .unwrap();

Pick specific suites

use rustls::crypto::CryptoProvider;

let mut provider = rustls::crypto::aws_lc_rs::default_provider();
provider.cipher_suites.insert(0, *rustls_ccm::TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8);

let config = rustls::ClientConfig::builder_with_provider(provider.into())
    .with_safe_default_protocol_versions()
    .unwrap();

Limitations

• ConnectionTrafficSecrets extraction is not supported — extract_keys returns UnsupportedOperationError for all CCM suites. SSLKEYLOGFILE-style secret export will not work when a CCM suite is negotiated.

How it works

The crate borrows key exchange (ECDHE), signature (ECDSA), hash (SHA-256), PRF, and HKDF implementations from the aws-lc-rs provider. Only the AEAD algorithm is replaced with a CCM implementation built on RustCrypto's aes and ccm crates.

License

MIT OR Apache-2.0