lib: [ZUC] fix LFSR update in 1 buffer implementation

For a specific scenario, LFSR was incorrectly updated when generating single buffer keystream, updating one of the LFSRs to 0, instead of 0x7fffffff. Fixes #144. Signed-off-by: Pablo de Lara <[email protected]>
intel · Feb 19, 2024 · e1526ab · e1526ab
1 parent dad3dfb
commit e1526ab
Showing 1 changed file with 4 additions and 3 deletions.
diff --git a/lib/x86_64/zuc_common.asm b/lib/x86_64/zuc_common.asm
@@ -235,9 +235,10 @@ mksection .text
     shr         rbx, 31
     add         rax, rbx
 
-    mov rbx, rax
-    sub rbx, 0x7FFFFFFF
-    cmovns rax, rbx
+    mov         rbx, rax
+    and         rax, 0x7FFFFFFF
+    shr         rbx, 31
+    add         rax, rbx
 
     ; LFSR_S16 = (LFSR_S15++) = eax
     mov         [rsi + (( 0 + %1) % 16)*4], eax