Correct PKINIT EC cert signature metadata

When generating CMS SignedData in PKINIT, check the certificate's
public key type and set the signatureAlgorithm field appropriately.
(This field is currently ignored by OpenSSL when verifying CMS
SignedData.)

ticket: 9111 (new)

src/plugins/preauth/pkinit/pkinit_crypto_openssl.c

@@ -1662,7 +1662,22 @@ cms_contentinfo_create(krb5_context context,                          /* IN */
     return retval;
 }
 
+/* Return the name ID of the signature algorithm for cert, assuming that the
+ * digest used is SHA-256 and the cert uses either an RSA or EC public key. */
+static int
+cert_sig_alg(X509 *cert)
+{
+    /* Use X509_get0_pubkey() when OpenSSL 1.0 support is removed. */
+    EVP_PKEY *pkey = X509_get_pubkey(cert);
+    int id;
 
+    if (pkey != NULL && EVP_PKEY_get_base_id(pkey) == EVP_PKEY_EC)
+        id = NID_ecdsa_with_SHA256;
+    else
+        id = NID_sha256WithRSAEncryption;
+    EVP_PKEY_free(pkey);
+    return id;
+}
 
 krb5_error_code
 cms_signeddata_create(krb5_context context,
@@ -1695,6 +1710,7 @@ cms_signeddata_create(krb5_context context,
     unsigned int alg_len = 0, digest_len = 0;
     unsigned char *y = NULL;
     ASN1_OBJECT *oid = NULL, *oid_copy;
+    int sig_alg_id;
 
     /* Start creating PKCS7 data. */
     if ((p7 = PKCS7_new()) == NULL)
@@ -1782,8 +1798,8 @@ cms_signeddata_create(krb5_context context,
         /* Set sig algs */
         if (p7si->digest_enc_alg->parameter != NULL)
             ASN1_TYPE_free(p7si->digest_enc_alg->parameter);
-        p7si->digest_enc_alg->algorithm =
-            OBJ_nid2obj(NID_sha256WithRSAEncryption);
+        sig_alg_id = cert_sig_alg(id_cryptoctx->my_cert);
+        p7si->digest_enc_alg->algorithm = OBJ_nid2obj(sig_alg_id);
         if (!(p7si->digest_enc_alg->parameter = ASN1_TYPE_new()))
             goto cleanup;
         p7si->digest_enc_alg->parameter->type = V_ASN1_NULL;