Add the CRC32 compensation attack detector that all other SSH

clients have had for ages and I forgot about. Of course I've got the
version with the buffer overflow fixed!

[originally from svn r1535]

ssh.h

@@ -72,6 +72,10 @@ typedef unsigned int word32;
 typedef unsigned int uint32;
 
 unsigned long crc32(const void *s, size_t len);
+unsigned long crc32_update(unsigned long crc_input, const void *s, size_t len);
+
+/* SSH CRC compensation attack detector */
+int detect_attack(unsigned char *buf, uint32 len, unsigned char *IV);
 
 typedef struct {
     uint32 h[4];