LibCrypto: Make a better ASN.1 parser

And use it to parse RSA keys.
As a bonus, this one shouldn't be reading out of bounds or messing with
the stack (as much) anymore.

Userland/Utilities/test-crypto.cpp

@@ -1970,8 +1970,9 @@ static void rsa_emsa_pss_test_create()
 
 static void rsa_test_der_parse()
 {
-    I_TEST((RSA | ASN1 DER / PEM encoded Key import));
-    auto privkey = R"(-----BEGIN RSA PRIVATE KEY-----
+    {
+        I_TEST((RSA | ASN1 PKCS1 DER / PEM encoded Key import));
+        auto privkey = R"(-----BEGIN RSA PRIVATE KEY-----
 MIIBOgIBAAJBAJsrIYHxs1YL9tpfodaWs1lJoMdF4kgFisUFSj6nvBhJUlmBh607AlgTaX0E
 DGPYycXYGZ2n6rqmms5lpDXBpUcCAwEAAQJAUNpPkmtEHDENxsoQBUXvXDYeXdePSiIBJhpU
 joNOYoR5R9z5oX2cpcyykQ58FC2vKKg+x8N6xczG7qO95tw5UQIhAN354CP/FA+uTeJ6KJ+i
@@ -1980,14 +1981,57 @@ IQCTjYI861Y+hjMnlORkGSdvWlTHUj6gjEOh4TlWeJzQoQIgAxMZOQKtxCZUuxFwzRq4xLRG
 nrDlBQpuxz7bwSyQO7UCIHrYMnDohgNbwtA5ZpW3H1cKKQQvueWm6sxW9P5sUrZ3
 -----END RSA PRIVATE KEY-----)";
 
-    Crypto::PK::RSA rsa(privkey);
-    if (rsa.public_key().public_exponent() == 65537) {
-        if (rsa.private_key().private_exponent() == "4234603516465654167360850580101327813936403862038934287300450163438938741499875303761385527882335478349599685406941909381269804396099893549838642251053393"_bigint) {
-            PASS;
-        } else
-            FAIL(Invalid private exponent);
-    } else {
-        FAIL(Invalid public exponent);
+        Crypto::PK::RSA rsa(privkey);
+        if (rsa.public_key().public_exponent() == 65537) {
+            if (rsa.private_key().private_exponent() == "4234603516465654167360850580101327813936403862038934287300450163438938741499875303761385527882335478349599685406941909381269804396099893549838642251053393"_bigint) {
+                PASS;
+            } else
+                FAIL(Invalid private exponent);
+        } else {
+            FAIL(Invalid public exponent);
+        }
+    }
+
+    {
+        I_TEST((RSA | ASN1 PKCS8 DER / PEM encoded Key import));
+        auto privkey = R"(-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----)";
+
+        Crypto::PK::RSA rsa(privkey);
+        if (rsa.public_key().public_exponent() == 65537) {
+            if (rsa.private_key().private_exponent() == "16848664331299797559656678180469464902267415922431923391961407795209879741791261105581093539484181644099608161661780611501562625272630894063592208758992911105496755004417051031019663332258403844985328863382168329621318366311519850803972480500782200178279692319955495383119697563295214236936264406600739633470565823022975212999060908747002623721589308539473108154612454595201561671949550531384574873324370774408913092560971930541734744950937900805812300970883306404011323308000168926094053141613790857814489531436452649384151085451448183385611208320292948291211969430321231180227006521681776197974694030147965578466993"_bigint) {
+                PASS;
+            } else
+                FAIL(Invalid private exponent);
+        } else {
+            FAIL(Invalid public exponent);
+        }
     }
 }