Implement X509_get_signature_info()

This is a slightly strange combination of OBJ_find_sigid_algs() and the
security level API necessary because OBJ_find_sigid_algs() on its own
isn't smart enough for the special needs of RSA-PSS and EdDSA.

The API extracts the hash's NID and the pubkey's NID from the certificate's
signatureAlgorithm and invokes special handlers for RSA-PSS and EdDSA
for retrieving the corresponding information. This isn't entirely free
for RSA-PSS, but for now we don't cache this information.

The security bits calculation is a bit hand-wavy, but that's something
that comes along with this sort of numerology.

ok jsing

1 files changed, 113 insertions, 0 deletions

diff --git a/src/lib/libcrypto/x509/x509_siginfo.c b/src/lib/libcrypto/x509/x509_siginfo.c
new file mode 100644
index 0000000000..9bbb133216
--- /dev/null
+++ b/src/lib/libcrypto/x509/x509_siginfo.c
@@ -0,0 +1,113 @@
+/*      $OpenBSD: x509_siginfo.c,v 1.1 2024/08/28 07:15:04 tb Exp $ */
+
+/*
+ * Copyright (c) 2024 Theo Buehler <tb@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <openssl/evp.h>
+#include <openssl/objects.h>
+#include <openssl/x509.h>
+
+#include "evp_local.h"
+
+#include "x509_internal.h"
+
+static int
+x509_find_sigid_algs(const X509 *x509, int *out_md_nid, int *out_pkey_nid)
+{
+        const ASN1_OBJECT *aobj;
+        int nid;
+
+        *out_md_nid = NID_undef;
+        *out_pkey_nid = NID_undef;
+
+        X509_ALGOR_get0(&aobj, NULL, NULL, x509->sig_alg);
+        if ((nid = OBJ_obj2nid(aobj)) == NID_undef)
+                return 0;
+
+        return OBJ_find_sigid_algs(nid, out_md_nid, out_pkey_nid);
+}
+
+int
+X509_get_signature_info(X509 *x509, int *out_md_nid, int *out_pkey_nid,
+    int *out_security_bits, uint32_t *out_flags)
+{
+        const EVP_MD *md;
+        int md_nid = NID_undef, pkey_nid = NID_undef, security_bits = -1;
+        uint32_t flags = 0;
+
+        if (out_md_nid != NULL)
+                *out_md_nid = md_nid;
+        if (out_pkey_nid != NULL)
+                *out_pkey_nid = pkey_nid;
+        if (out_security_bits != NULL)
+                *out_security_bits = security_bits;
+        if (out_flags != NULL)
+                *out_flags = flags;
+
+        if (!x509v3_cache_extensions(x509))
+                goto err;
+
+        if (!x509_find_sigid_algs(x509, &md_nid, &pkey_nid))
+                goto err;
+
+        /*
+         * If md_nid == NID_undef, this means we need to consult the ameth.
+         * Handlers are available for EdDSA and RSA-PSS. No other signature
+         * algorithm with NID_undef should appear in a certificate.
+         */
+        if (md_nid == NID_undef) {
+                const EVP_PKEY_ASN1_METHOD *ameth;
+
+                if ((ameth = EVP_PKEY_asn1_find(NULL, pkey_nid)) == NULL ||
+                    ameth->signature_info == NULL)
+                        goto err;
+
+                if (!ameth->signature_info(x509->sig_alg, &md_nid, &pkey_nid,
+                    &security_bits, &flags))
+                        goto err;
+
+                goto done;
+        }
+
+        /* XXX - OpenSSL 3 special cases SHA-1 (63 bits) and MD5 (39 bits). */
+        if ((md = EVP_get_digestbynid(md_nid)) == NULL)
+                goto err;
+
+        /* Assume 4 bits of collision resistance per octet. */
+        if ((security_bits = EVP_MD_size(md)) <= 0)
+                goto err;
+        security_bits *= 4;
+
+        if (md_nid == NID_sha1 || md_nid == NID_sha256 ||
+            md_nid == NID_sha384 || md_nid == NID_sha512)
+                flags |= X509_SIG_INFO_TLS;
+
+        flags |= X509_SIG_INFO_VALID;
+
+ done:
+        if (out_md_nid != NULL)
+                *out_md_nid = md_nid;
+        if (out_pkey_nid != NULL)
+                *out_pkey_nid = pkey_nid;
+        if (out_security_bits != NULL)
+                *out_security_bits = security_bits;
+        if (out_flags != NULL)
+                *out_flags = flags;
+
+ err:
+        return (flags & X509_SIG_INFO_VALID) != 0;
+}
+LCRYPTO_ALIAS(X509_get_signature_info);