From: Nick Mathewson <nickm@torproject.org>
Date: Thu, 5 Jun 2025 20:12:24 +0000 (-0400)
Subject: cgo: Use the correct operation to re-align AES.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bddd835d6938bf2489ff8970dd3e172444f73052;p=thirdparty%2Ftor.git

cgo: Use the correct operation to re-align AES.

By accident, this doesn't cause a bug, since 480 = 15*16*2.
Still, it's better to avoid problems in the future.

Closes #41091.
---

diff --git a/src/core/crypto/relay_crypto_cgo.c b/src/core/crypto/relay_crypto_cgo.c
index d3622de228..1e900861fe 100644
--- a/src/core/crypto/relay_crypto_cgo.c
+++ b/src/core/crypto/relay_crypto_cgo.c
@@ -190,7 +190,7 @@ cgo_prf_xor_t0(cgo_prf_t *prf, const uint8_t *input,
   // Re-align the cipher.
   //
   // This approach is faster than EVP_CIPHER_set_num!
-  const int ns = 16 - (PRF_T0_DATA_LEN % 0xf);
+  const int ns = 16 - (PRF_T0_DATA_LEN & 0xf);
   // We're not using the hash for anything, so it's okay to overwrite
   aes_crypt_inplace(prf->k, (char*)hash,  ns);
 }