crypto: Introduce x509 utils

An utility function for getting fingerprint from X.509 certificate
has been introduced. Implementation only provided using gnutls.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
[DB: fixed missing gnutls_x509_crt_deinit in success path]
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/meson.build

@@ -24,6 +24,10 @@ crypto_ss.add(files(
   'rsakey.c',
 ))
 
+if gnutls.found()
+  crypto_ss.add(files('x509-utils.c'))
+endif
+
 if nettle.found()
   crypto_ss.add(nettle, files('hash-nettle.c', 'hmac-nettle.c', 'pbkdf-nettle.c'))
   if hogweed.found()

crypto/x509-utils.c

@@ -0,0 +1,76 @@
+/*
+ * X.509 certificate related helpers
+ *
+ * Copyright (c) 2024 Dorjoy Chowdhury <dorjoychy111@gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "crypto/x509-utils.h"
+#include <gnutls/gnutls.h>
+#include <gnutls/crypto.h>
+#include <gnutls/x509.h>
+
+static const int qcrypto_to_gnutls_hash_alg_map[QCRYPTO_HASH_ALG__MAX] = {
+    [QCRYPTO_HASH_ALG_MD5] = GNUTLS_DIG_MD5,
+    [QCRYPTO_HASH_ALG_SHA1] = GNUTLS_DIG_SHA1,
+    [QCRYPTO_HASH_ALG_SHA224] = GNUTLS_DIG_SHA224,
+    [QCRYPTO_HASH_ALG_SHA256] = GNUTLS_DIG_SHA256,
+    [QCRYPTO_HASH_ALG_SHA384] = GNUTLS_DIG_SHA384,
+    [QCRYPTO_HASH_ALG_SHA512] = GNUTLS_DIG_SHA512,
+    [QCRYPTO_HASH_ALG_RIPEMD160] = GNUTLS_DIG_RMD160,
+};
+
+int qcrypto_get_x509_cert_fingerprint(uint8_t *cert, size_t size,
+                                      QCryptoHashAlgorithm alg,
+                                      uint8_t *result,
+                                      size_t *resultlen,
+                                      Error **errp)
+{
+    int ret = -1;
+    int hlen;
+    gnutls_x509_crt_t crt;
+    gnutls_datum_t datum = {.data = cert, .size = size};
+
+    if (alg >= G_N_ELEMENTS(qcrypto_to_gnutls_hash_alg_map)) {
+        error_setg(errp, "Unknown hash algorithm");
+        return -1;
+    }
+
+    if (result == NULL) {
+        error_setg(errp, "No valid buffer given");
+        return -1;
+    }
+
+    gnutls_x509_crt_init(&crt);
+
+    if (gnutls_x509_crt_import(crt, &datum, GNUTLS_X509_FMT_PEM) != 0) {
+        error_setg(errp, "Failed to import certificate");
+        goto cleanup;
+    }
+
+    hlen = gnutls_hash_get_len(qcrypto_to_gnutls_hash_alg_map[alg]);
+    if (*resultlen < hlen) {
+        error_setg(errp,
+                   "Result buffer size %zu is smaller than hash %d",
+                   *resultlen, hlen);
+        goto cleanup;
+    }
+
+    if (gnutls_x509_crt_get_fingerprint(crt,
+                                        qcrypto_to_gnutls_hash_alg_map[alg],
+                                        result, resultlen) != 0) {
+        error_setg(errp, "Failed to get fingerprint from certificate");
+        goto cleanup;
+    }
+
+    ret = 0;
+
+ cleanup:
+    gnutls_x509_crt_deinit(crt);
+    return ret;
+}

include/crypto/x509-utils.h

@@ -0,0 +1,22 @@
+/*
+ * X.509 certificate related helpers
+ *
+ * Copyright (c) 2024 Dorjoy Chowdhury <dorjoychy111@gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#ifndef QCRYPTO_X509_UTILS_H
+#define QCRYPTO_X509_UTILS_H
+
+#include "crypto/hash.h"
+
+int qcrypto_get_x509_cert_fingerprint(uint8_t *cert, size_t size,
+                                      QCryptoHashAlgorithm hash,
+                                      uint8_t *result,
+                                      size_t *resultlen,
+                                      Error **errp);
+
+#endif