From 9c8f3ec67b3d8413ec0ede19cb7a264121b0277f Mon Sep 17 00:00:00 2001
From: Mounir IDRASSI <mounir.idrassi@amcrypto.jp>
Date: Sat, 17 Oct 2026 21:41:03 +0900
Subject: [PATCH] Crypto: fix ChaCha partial block continuation

Count consumed input bytes so short updates don't skip unused keystream.
Reset the saved offset when the block is exhausted.

Reported by @router0mail.
---
 src/Crypto/chacha256.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Crypto/chacha256.c b/src/Crypto/chacha256.c
index 685f7886..2dd7b521 100644
--- a/src/Crypto/chacha256.c
+++ b/src/Crypto/chacha256.c
@@ -151,12 +151,14 @@ static VC_INLINE void do_encrypt(const unsigned char* in, size_t len, unsigned c
     size_t i = 0, pos = *posPtr;
     if (pos)
     {
-        while (pos < len && pos < 64)
+        while (i < len && pos < 64)
         {
             out[i] = in[i] ^ ((unsigned char*)block)[pos++];
             ++i;
         }
         len -= i;
+        if (pos == 64)
+            pos = 0;
     }
     if (len)
         pos = 0;