-u: like -m, but decrypt to verify MAC, see if it's valid then decrypt to dst.

[tfcrypt.git] / tfc_error.c

diff --git a/tfc_error.c b/tfc_error.c
index 17efe74a443659633b103c507bc1a4b4240a8f2c..2108dc519a02a1822a305355c546ec39fe9526f8 100644 (file)
--- a/tfc_error.c
+++ b/tfc_error.c
@@ -269,7 +269,11 @@ void usage(void)
        tfc_say("    -: read a detached MAC signature from stdin,");
        tfc_say("    drop: do not verify attached MAC, if any, and drop it from output.");
        tfc_say("  -m: just verify MAC provided with -M. Do not write output file.");
-       tfc_say("    This option must be specified after -M.");
+       tfc_say("  -u: almost same as -m, but turns on MAC pre-test mode, when verified");
+       tfc_say("    signature enables writing output file. It is useful when decrypting small texts.");
+       tfc_say("    The source must be a seekable file, otherwise this mode will be disabled.");
+       tfc_say("    In this mode, decryption is done twice and verification done once.");
+       tfc_say("    Both -m and -u options must be specified after -M.");
        tfc_say("  -E how: how to behave on I/O errors (both src or dst):");
        tfc_say("    exit: print error if not quiet, then exit,");
        tfc_say("    cont: print error if not quiet, then continue,");