Ignore the digest in req app if using EdDSA

This follows on from the previous commit, and makes the same change to
ignore the digest if we are using EdDSA.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6901)

2 files changed, 15 insertions, 6 deletions

diff --git a/apps/req.c b/apps/req.c
index 48f3a3ab98..08a1468ef4 100644
--- a/apps/req.c
+++ b/apps/req.c
@@ -1601,10 +1601,19 @@ static int do_sign_init(EVP_MD_CTX *ctx, EVP_PKEY *pkey,
                         const EVP_MD *md, STACK_OF(OPENSSL_STRING) *sigopts)
 {
     EVP_PKEY_CTX *pkctx = NULL;
-    int i;
+    int i, def_nid;
 
     if (ctx == NULL)
         return 0;
+    /*
+     * EVP_PKEY_get_default_digest_nid() returns 2 if the digest is mandatory
+     * for this algorithm.
+     */
+    if (EVP_PKEY_get_default_digest_nid(pkey, &def_nid) == 2
+            && def_nid == NID_undef) {
+        /* The signing algorithm requires there to be no digest */
+        md = NULL;
+    }
     if (!EVP_DigestSignInit(ctx, &pkctx, md, NULL, pkey))
         return 0;
     for (i = 0; i < sk_OPENSSL_STRING_num(sigopts); i++) {
diff --git a/doc/man1/req.pod b/doc/man1/req.pod
index db467bba17..51f3ec4494 100644
--- a/doc/man1/req.pod
+++ b/doc/man1/req.pod
@@ -209,7 +209,7 @@ the configuration file.
 
 Some public key algorithms may override this choice. For instance, DSA
 signatures always use SHA1, GOST R 34.10 signatures always use
-GOST R 34.11-94 (B<-md_gost94>).
+GOST R 34.11-94 (B<-md_gost94>), Ed25519 and Ed448 never use any digest.
 
 =item B<-config filename>
 
@@ -394,10 +394,10 @@ option. For compatibility B<encrypt_rsa_key> is an equivalent option.
 
 =item B<default_md>
 
-This option specifies the digest algorithm to use.
-Any digest supported by the OpenSSL B<dgst> command can be used.
-If not present then MD5 is used.
-This option can be overridden on the command line.
+This option specifies the digest algorithm to use. Any digest supported by the
+OpenSSL B<dgst> command can be used. This option can be overridden on the
+command line. Certain signing algorithms (i.e. Ed25519 and Ed448) will ignore
+any digest that has been set.
 
 =item B<string_mask>