[project @ Arch-1:robey@lag.net--2003-public%secsh--dev--1.0--patch-4]

change kex-gex server code to generate primes by hand
added a util function "generate_prime" to compare to the incredibly slow C
version, but it's no faster of course.  i think kex-gex from the server is
just not going to be feasible without having a separate thread generate some
primes in the background to have handy when a request comes in.  so in short,
this still doesn't work.

also i put bit_length into util and a tb_strings function which gets stack
traceback info and splits it into a list of strings.

1 files changed, 29 insertions, 1 deletions

diff --git a/util.py b/util.py
index 28349721..fd78af38 100644
--- a/util.py
+++ b/util.py
@@ -1,6 +1,7 @@
 #!/usr/bin/python
 
-import struct
+import sys, struct, traceback
+from Crypto.Util import number
 
 def inflate_long(s, always_positive=0):
     "turns a normalized byte string into a long-int (adapted from Crypto.Util.number)"
@@ -87,3 +88,30 @@ def safe_string(s):
     return out
 
 # ''.join([['%%%02X' % ord(c), c][(ord(c) >= 32) and (ord(c) <= 127)] for c in s])
+
+def bit_length(n):
+    norm = deflate_long(n, 0)
+    hbyte = ord(norm[0])
+    bitlen = len(norm) * 8
+    while not (hbyte & 0x80):
+        hbyte <<= 1
+        bitlen -= 1
+    return bitlen
+
+def generate_prime(bits, randpool):
+    hbyte_mask = pow(2, bits % 8) - 1
+    x = randpool.get_bytes((bits+7) // 8)
+    if hbyte_mask > 0:
+        x = chr(ord(x[0]) & hbyte_mask) + x[1:]
+    n = inflate_long(x, 1)
+    n |= 1
+    n |= (1 << (bits - 1))
+    while 1:
+        # loop catches the case where we increment n into a higher bit-range
+        while not number.isPrime(n):
+            n += 2
+        if bit_length(n) == bits:
+            return n
+
+def tb_strings():
+    return ''.join(traceback.format_exception(*sys.exc_info())).split('\n')