# Cryptographic providers
RustCrypto is the default. Enable `aws-lc-fips` to additionally compile the official
`aws-lc-rs` wrapper with its `fips` feature and without its default features. This
links the AWS-LC FIPS module, not the ordinary AWS-LC module. It requires the native
toolchain described in the [AWS build requirements](https://aws.github.io/aws-lc-rs/requirements/index.html).
Provider choice is explicit operation context, independent of the immutable security
policy. Pass `AwsLcFipsProvider` to `SignContext::provider`, `VerifyContext::provider`,
`EncryptedDataBuilder::provider`, or `DecryptContext::provider`. Use
`KeyInventory::signing_key_with_provider` and
`KeyInventory::decryption_resolver_with_provider` to import private material directly
into the chosen engine. Native private handles reject use through another provider;
public SPKI bytes can be verified by either engine. There is no automatic fallback.
Key-container decoding remains a distinct inventory import boundary: encrypted
PKCS#8 and PKCS#12 password-based container processing uses the existing RustCrypto
importer. Selecting AWS-LC does not turn that importer into an approved FIPS service.
The CLI's generic `--privkey-pem`/`--privkey-der` options also preserve traditional
RSA PKCS#1 and EC SEC1 containers independently of the provider. Traditional
OpenSSL encrypted PEM is decrypted at this same container boundary. Normalization
is resource-bounded; selecting AWS-LC still imports the resulting key into its
native handle without falling back to RustCrypto for the requested operation.
Explicit `--pkcs8-pem`/`--pkcs8-der` options remain PKCS#8-only. Missing or incorrect
passwords are terminal, including during lax key search.
Applications requiring an exclusively native secret-processing boundary should supply
plain PKCS#8 directly to `AwsLcSigningKey::from_pkcs8_der` or
`AwsLcRsaPrivateKey::from_pkcs8_der`, rather than using protected-container import.
The native `xmlsec1` accepts `--crypto aws-lc-fips` when this feature is compiled.
Without it, that selection is an explicit unavailable-provider error.
## Mechanisms
`legacy-algorithms` adds RustCrypto MD5/RIPEMD-160 signatures and digests, AES-192
content encryption and key wrap, TripleDES content encryption and CMS wrap, and RSA-1.5
transport. All operations still go through `CryptoProvider` and require explicit library policy
permission. The AWS FIPS adapter reports these optional mechanisms unavailable; compiling both
providers never falls back to RustCrypto. This describes the adapter's supported operations, not
every primitive present in the underlying AWS-LC library or an approved-service claim.
The AWS provider supports SHA-1/SHA-2 and SHA3-256/384/512 digests; RSA PKCS#1 v1.5
signing with SHA-256/384/512 and verification with those digests or SHA-1; native
ECDSA curve/digest combinations exposed by AWS-LC; AES-128/256 CBC and GCM;
AES-128/256 key wrap; and RSA-OAEP with SHA-1/256/384/512 when MGF uses the same
digest. RSA-OAEP labels are preserved. Certificate and CRL verification uses DER
ECDSA encoding rather than XMLDSig's fixed-width encoding.
SHA3-224, DSA, HMAC signatures, EdDSA, post-quantum signatures, RSA-PSS certificate
signatures, mixed-digest OAEP, and unavailable ECDSA combinations return unsupported
errors. Consult `CryptoProvider::supports` before requesting a mechanism; actual
key parameters are checked at import/use as well. RSA PKCS#1 verification supports
2048-8192-bit moduli, including certificate and CRL issuer keys. Keys outside this
native range return unsupported rather than a signature mismatch, even when caller
policy permits their size. Availability never overrides policy.
## FIPS boundary
Linking a FIPS module is not certification of xml-sec or of the caller's application.
The exact module version, validated operating environment, approved service, and
deployment requirements must match the applicable AWS security policy and validation.
`AwsLcFipsProvider::module_version` and `fips_module_version` expose the linked
module's own version information for deployment diagnostics.
The module also exposes mechanisms that are not approved services. This adapter does
not attest an approved-service indicator or relax algorithm policy based on its name.
See [AWS-LC FIPS documentation](https://github.com/aws/aws-lc/blob/main/crypto/fipsmodule/FIPS.md)
and [supported platforms](https://aws.github.io/aws-lc-rs/platform_support.html).
Default pure-Rust builds and the alloc-only XML-input path remain independent of this
optional native dependency. Tests compare supported primitives between engines and
exercise complete XML operation paths, malformed inputs, tampering, and provider binding.