`keys/parse-spki`

Purpose

Parses an X.509 SubjectPublicKeyInfo per RFC 5280 §4.1 + Appendix A and unwraps the inner PKCS#1 RSAPublicKey. SPKI is the canonical wire format for RSA public keys in TLS certificates (Certificate.tbsCertificate.subjectPublicKeyInfo), JWK headers (x5c/x5t#S256 reference chains), and the WebAuthn TPM attestation statement.

The parser enforces the 1.2.840.113549.1.1.1 rsaEncryption algorithm OID and the canonical NULL algorithm parameters per RFC 3279 §2.3.1.

Features

DER outer-SEQUENCE → AlgorithmIdentifier → BIT STRING walk.
Algorithm OID equality check against OID_RSA_ENCRYPTION.
NULL algorithm-parameters enforcement (RFC 3279 §2.3.1).
Delegates inner PKCS#1 parse to parseRsaPublicKeyPkcs1.

Usage: Basic Example

import { parseRsaPublicKeySpki } from "@suaveplan/crypto-rsa";

const key = parseRsaPublicKeySpki(spkiDerBytes);

Usage: Advanced Example

import { parseRsaPublicKeySpki } from "@suaveplan/crypto-rsa";

// SPKI carrying an EC OID rejects with UNSUPPORTED_FORMAT.
try {
    parseRsaPublicKeySpki(ecSpkiBytes);
} catch (error) {
    if (error instanceof CryptoRsaError && error.code === "CRYPTO_RSA.UNSUPPORTED_FORMAT") {
        // dispatch to @suaveplan/crypto-curve
    }
}

API Reference

`parseRsaPublicKeySpki(bytes: Uint8Array): RsaPublicKey`

Throws CryptoRsaError(CRYPTO_RSA.UNSUPPORTED_FORMAT) for non-RSA OIDs. Throws CryptoRsaError(CRYPTO_RSA.INVALID_KEY) on structural problems (missing fields, trailing data, unused-bits ≠ 0 in the BIT STRING).

Implementation Notes

The BIT STRING payload is copied (defensive copy in DerReader.readBitString) so the inner PKCS#1 reader never aliases the input buffer. This costs one allocation per parse but eliminates a class of subtle bugs where downstream mutation of the inner buffer would corrupt the SPKI input.

alg.assertEnd() and outer.assertEnd() together guarantee no extra fields slipped through. RFC 3279 forbids extra parameters in the rsaEncryption algorithm identifier, and RFC 5280 forbids extra fields in SubjectPublicKeyInfo.

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keys/parse-spki