commit 858bc65d7485b8af9c49e96d0cf0bf803606a120
author Chien Wong <m@xv97.com> Mon Jan 22 20:47:26 2024 +0800
committer Chien Wong <m@xv97.com> Mon Jan 22 20:47:26 2024 +0800
tree c1eedce7a8f6d743166cbac2357ce9cd1bdf1b26
parent bf4b5ed7a4e02358cb008bb43c20f5f3c309b7c1

Add comment on impossible overflows

Signed-off-by: Chien Wong <m@xv97.com>

library/gcm.c

diff --git a/library/gcm.c b/library/gcm.c
index b31003f..337145b 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -542,6 +542,9 @@
     (void) output_size;
     *output_length = 0;
 
+    /* Total length is restricted to 2^39 - 256 bits, ie 2^36 - 2^5 bytes
+     * and AD length is restricted to 2^64 bits, ie 2^61 bytes so neither of
+     * the two multiplications would overflow. */
     orig_len = ctx->len * 8;
     orig_add_len = ctx->add_len * 8;