We calculate checksum on plain text, so we must have already decrypt it, which means...

diff --git a/libfreerdp-core/security.c b/libfreerdp-core/security.c
index e003b21..8df8a65 100644 (file)
--- a/libfreerdp-core/security.c
+++ b/libfreerdp-core/security.c
@@ -264,7 +264,13 @@ void security_salted_mac_signature(rdpRdp *rdp, uint8* data, uint32 length, bool
        if (encryption)
                security_uint32_le(use_count_le, rdp->encrypt_use_count);
        else
-               security_uint32_le(use_count_le, rdp->decrypt_use_count);
+       {
+               /*
+                * We calculate checksum on plain text, so we must have already
+                * decrypt it, which means decrypt_use_count is off by one.
+                */
+               security_uint32_le(use_count_le, rdp->decrypt_use_count - 1);
+       }
 
        /* SHA1_Digest = SHA1(MACKeyN + pad1 + length + data) */
        sha1 = crypto_sha1_init();