Initial Commit

packages/security-stack/crypto/crypto-rsa/src/keys/parse-pkcs1-public.ts

@@ -0,0 +1,48 @@
+import { DerReader } from "../asn1/reader.js";
+import { CRYPTO_RSA_CODES, CryptoRsaError } from "../errors/errors.js";
+import type { RsaPublicKey } from "./keys.types.js";
+
+/**
+ * Parse a DER-encoded PKCS#1 `RSAPublicKey ::= SEQUENCE { modulus INTEGER,
+ * publicExponent INTEGER }` per RFC 8017 Appendix A.1.1.
+ *
+ * Validates that the public exponent is odd and `>= 3`, matching the
+ * conformance requirement in the spec delta.
+ */
+export function parseRsaPublicKeyPkcs1(bytes: Uint8Array): RsaPublicKey {
+    const reader = new DerReader(bytes);
+    const seq = reader.readSequence();
+    const n = seq.readInteger();
+    const e = seq.readInteger();
+    seq.assertEnd();
+    reader.assertEnd();
+    return finalisePublicKey(n, e);
+}
+
+/**
+ * Internal: validate `(n, e)` and compute `bitLength`. Used by SPKI / JWK
+ * parsers as well as the PKCS#1 path.
+ */
+export function finalisePublicKey(n: bigint, e: bigint): RsaPublicKey {
+    if (n <= 0n) {
+        throw new CryptoRsaError(
+            CRYPTO_RSA_CODES.INVALID_KEY,
+            "error.crypto-rsa.invalid-key.modulus"
+        );
+    }
+    if (e < 3n) {
+        throw new CryptoRsaError(
+            CRYPTO_RSA_CODES.INVALID_KEY,
+            "error.crypto-rsa.invalid-key.exponent-too-small",
+            { context: { e: e.toString() } }
+        );
+    }
+    if ((e & 1n) === 0n) {
+        throw new CryptoRsaError(
+            CRYPTO_RSA_CODES.INVALID_KEY,
+            "error.crypto-rsa.invalid-key.exponent-even"
+        );
+    }
+    const bitLength = n.toString(2).length;
+    return { n, e, bitLength };
+}