diff -up gnupg-2.2.20/g10/gpg.c.file-is-digest gnupg-2.2.20/g10/gpg.c

--- gnupg-2.2.20/g10/gpg.c.file-is-digest	2020-04-14 16:33:42.630269318 +0200

+++ gnupg-2.2.20/g10/gpg.c	2020-04-14 16:34:46.455100086 +0200

@@ -380,6 +380,7 @@ enum cmd_and_opt_values

     oTTYtype,

     oLCctype,

     oLCmessages,

+    oFileIsDigest,

     oXauthority,

     oGroup,

     oUnGroup,

@@ -831,6 +832,7 @@ static ARGPARSE_OPTS opts[] = {

   ARGPARSE_s_s (oPersonalCompressPreferences,

                                          "personal-compress-preferences", "@"),

   ARGPARSE_s_s (oFakedSystemTime, "faked-system-time", "@"),

+  ARGPARSE_s_n (oFileIsDigest, "file-is-digest", "@"),

   ARGPARSE_s_s (oWeakDigest, "weak-digest","@"),

   ARGPARSE_s_n (oUnwrap, "unwrap", "@"),

   ARGPARSE_s_n (oOnlySignTextIDs, "only-sign-text-ids", "@"),

@@ -2419,6 +2421,7 @@ main (int argc, char **argv)

     opt.keyid_format = KF_NONE;

     opt.def_sig_expire = "0";

     opt.def_cert_expire = "0";

+    opt.file_is_digest = 0;

     gnupg_set_homedir (NULL);

     opt.passphrase_repeat = 1;

     opt.emit_version = 0;

@@ -2997,6 +3000,7 @@ main (int argc, char **argv)

 	    opt.verify_options&=~VERIFY_SHOW_PHOTOS;

 	    break;

 	  case oPhotoViewer: opt.photo_viewer = pargs.r.ret_str; break;

+	  case oFileIsDigest: opt.file_is_digest = 1; break;

           case oDisableSignerUID: opt.flags.disable_signer_uid = 1; break;

           case oIncludeKeyBlock:  opt.flags.include_key_block = 1; break;

diff -up gnupg-2.2.20/g10/options.h.file-is-digest gnupg-2.2.20/g10/options.h

--- gnupg-2.2.20/g10/options.h.file-is-digest	2020-03-14 19:54:05.000000000 +0100

+++ gnupg-2.2.20/g10/options.h	2020-04-14 16:33:42.634269245 +0200

@@ -202,6 +202,7 @@ struct

   int no_auto_check_trustdb;

   int preserve_permissions;

   int no_homedir_creation;

+  int file_is_digest;

   struct groupitem *grouplist;

   int mangle_dos_filenames;

   int enable_progress_filter;

diff -up gnupg-2.2.20/g10/sign.c.file-is-digest gnupg-2.2.20/g10/sign.c

--- gnupg-2.2.20/g10/sign.c.file-is-digest	2020-03-14 19:35:46.000000000 +0100

+++ gnupg-2.2.20/g10/sign.c	2020-04-14 16:36:54.661751422 +0200

@@ -40,6 +40,7 @@

 #include "pkglue.h"

 #include "../common/sysutils.h"

 #include "call-agent.h"

+#include "../common/host2net.h"

 #include "../common/mbox-util.h"

 #include "../common/compliance.h"

@@ -834,6 +835,8 @@ write_signature_packets (ctrl_t ctrl,

       if (duration || opt.sig_policy_url

           || opt.sig_notations || opt.sig_keyserver_url)

         sig->version = 4;

+	  else if (opt.file_is_digest)

+        sig->version = 3;

       else

         sig->version = pk->version;

@@ -860,8 +863,11 @@ write_signature_packets (ctrl_t ctrl,

           else

             err = 0;

         }

-      hash_sigversion_to_magic (md, sig);

-      gcry_md_final (md);

+

+      if (!opt.file_is_digest) {

+	hash_sigversion_to_magic (md, sig);

+	gcry_md_final (md);

+      }

       if (!err)

         err = do_sign (ctrl, pk, sig, md, hash_for (pk), cache_nonce, 0);

@@ -924,6 +930,8 @@ sign_file (ctrl_t ctrl, strlist_t filena

     SK_LIST sk_rover = NULL;

     int multifile = 0;

     u32 duration=0;

+    int sigclass = 0x00;

+    u32 timestamp = 0;

     pfx = new_progress_context ();

     afx = new_armor_context ();

@@ -941,7 +949,16 @@ sign_file (ctrl_t ctrl, strlist_t filena

 	fname = NULL;

     if( fname && filenames->next && (!detached || encryptflag) )

-	log_bug("multiple files can only be detached signed");

+	log_bug("multiple files can only be detached signed\n");

+

+    if (opt.file_is_digest && (multifile || !fname))

+	log_bug("file-is-digest only works with one file\n");

+    if (opt.file_is_digest && !detached)

+	log_bug("file-is-digest can only write detached signatures\n");

+    if (opt.file_is_digest && !opt.def_digest_algo)

+	log_bug("file-is-digest needs --digest-algo\n");

+    if (opt.file_is_digest && opt.textmode)

+	log_bug("file-is-digest doesn't work with --textmode\n");

     if(encryptflag==2

        && (rc=setup_symkey(&efx.symkey_s2k,&efx.symkey_dek)))

@@ -962,7 +979,7 @@ sign_file (ctrl_t ctrl, strlist_t filena

       goto leave;

     /* prepare iobufs */

-    if( multifile )  /* have list of filenames */

+    if( multifile || opt.file_is_digest)  /* have list of filenames */

 	inp = NULL; /* we do it later */

     else {

       inp = iobuf_open(fname);

@@ -1100,7 +1117,7 @@ sign_file (ctrl_t ctrl, strlist_t filena

     for (sk_rover = sk_list; sk_rover; sk_rover = sk_rover->next)

       gcry_md_enable (mfx.md, hash_for (sk_rover->pk));

-    if( !multifile )

+    if( !multifile && !opt.file_is_digest )

 	iobuf_push_filter( inp, md_filter, &mfx );

     if( detached && !encryptflag)

@@ -1155,6 +1172,8 @@ sign_file (ctrl_t ctrl, strlist_t filena

     write_status_begin_signing (mfx.md);

+    sigclass = opt.textmode && !outfile? 0x01 : 0x00;

+

     /* Setup the inner packet. */

     if( detached ) {

 	if( multifile ) {

@@ -1195,6 +1214,45 @@ sign_file (ctrl_t ctrl, strlist_t filena

 	    if( opt.verbose )

               log_printf ("\n");

 	}

+	else if (opt.file_is_digest) {

+	    byte *mdb, ts[5];

+	    size_t mdlen;

+	    const char *fp;

+	    int c, d;

+

+	    gcry_md_final(mfx.md);

+	    /* this assumes gcry_md_read returns the same buffer */

+	    mdb = gcry_md_read(mfx.md, opt.def_digest_algo);

+		mdlen = gcry_md_get_algo_dlen(opt.def_digest_algo);

+	    if (strlen(fname) != mdlen * 2 + 11)

+	        log_bug("digests must be %zu + @ + 5 bytes\n", mdlen);

+	    d = -1;

+	    for (fp = fname ; *fp; ) {

+		c = *fp++;

+		if (c >= '0' && c <= '9')

+		    c -= '0';

+		else if (c >= 'a' && c <= 'f')

+		    c -= 'a' - 10;

+		else if (c >= 'A' && c <= 'F')

+		    c -= 'A' - 10;

+		else

+		    log_bug("filename is not hex\n");

+		if (d >= 0) {

+		    *mdb++ = d << 4 | c;

+		    c = -1;

+		    if (--mdlen == 0) {

+			mdb = ts;

+			if (*fp++ != '@')

+			    log_bug("missing time separator\n");

+		    }

+		}

+		d = c;

+	    }

+	    sigclass = ts[0];

+	    if (sigclass != 0x00 && sigclass != 0x01)

+		log_bug("bad cipher class\n");

+	    timestamp = buf32_to_u32(ts + 1);

+	}

 	else {

 	    /* read, so that the filter can calculate the digest */

 	    while( iobuf_get(inp) != -1 )

@@ -1213,8 +1271,8 @@ sign_file (ctrl_t ctrl, strlist_t filena

     /* write the signatures */

     rc = write_signature_packets (ctrl, sk_list, out, mfx.md,

-                                  opt.textmode && !outfile? 0x01 : 0x00,

-				  0, duration, detached ? 'D':'S', NULL);

+                                  sigclass,

+				  timestamp, duration, detached ? 'D':'S', NULL);

     if( rc )

         goto leave;