merge fixes from PuTTY import.c toint() from misc.c (revids are from hggit conversion) changeset: 4620:60a336a6c85c user: Simon Tatham <[email protected]> date: Thu Feb 25 20:26:33 2016 +0000 files: import.c description: Fix potential segfaults in reading OpenSSH's ASN.1 key format. The length coming back from ber_read_id_len might have overflowed, so treat it as potentially negative. Also, while I'm here, accumulate it inside ber_read_id_len as an unsigned, so as to avoid undefined behaviour on integer overflow, and toint() it before return. Thanks to Hanno Böck for spotting this, with the aid of AFL. (cherry picked from commit 5b7833cd474a24ec098654dcba8cb9509f3bf2c1) Conflicts: import.c (cherry-picker's note: resolving the conflict involved removing an entire section of the original commit which fixed ECDSA code not present on this branch) changeset: 4619:9c6c638d98d8 user: Simon Tatham <[email protected]> date: Sun Jul 14 10:45:54 2013 +0000 files: import.c ssh.c sshdss.c sshpubk.c sshrsa.c description: Tighten up a lot of casts from unsigned to int which are read by one of the GET_32BIT macros and then used as length fields. Missing bounds checks against zero have been added, and also I've introduced a helper function toint() which casts from unsigned to int in such a way as to avoid C undefined behaviour, since I'm not sure I trust compilers any more to do the obviously sensible thing. [originally from svn r9918] changeset: 4618:3957829f24d3 user: Simon Tatham <[email protected]> date: Mon Jul 08 22:36:04 2013 +0000 files: import.c sshdss.c sshrsa.c description: Add an assortment of extra safety checks. [originally from svn r9896] changeset: 4617:2cddee0bce12 user: Jacob Nevins <[email protected]> date: Wed Dec 07 00:24:45 2005 +0000 files: import.c description: Institutional failure to memset() things pointed at rather than pointers. Things should now be zeroed and memory not leaked. Spotted by Brant Thomsen. [originally from svn r6476] changeset: 4616:24ac78a9c71d user: Simon Tatham <[email protected]> date: Wed Feb 11 13:58:27 2004 +0000 files: import.c description: Jacob's last-minute testing found a couple of trivial bugs in import.c, and my attempts to reproduce them in cmdgen found another one there :-) [originally from svn r3847] changeset: 4615:088d39a73db0 user: Simon Tatham <[email protected]> date: Thu Jan 22 18:52:49 2004 +0000 files: import.c description: Placate some gcc warnings. [originally from svn r3761] changeset: 4614:e4288bad4d93 parent: 1758:108b8924593d user: Simon Tatham <[email protected]> date: Fri Oct 03 21:21:23 2003 +0000 files: import.c description: My ASN.1 decoder returned wrong IDs for anything above 0x1E! Good job it's never had to yet. Ahem. [originally from svn r3479]

Tech Note 0003
Minimizing Memory Usage
Tom St Denis

Introduction
------------

For the most part the library can get by with around 20KB of stack and about 32KB of heap even if you use the
public key functions.  If all you plan on using are the hashes and ciphers than only about 1KB of stack is required
and no heap.

To save space all of the symmetric key scheduled keys are stored in a union called "symmetric_key".  This means the 
size of a symmetric_key is the size of the largest scheduled key.  By removing the ciphers you don't use from
the build you can minimize the size of this structure.  For instance, by removing both Twofish and Blowfish the
size reduces to 768 bytes from the 4,256 bytes it would have been (on a 32-bit platform).  Or if you remove
Blowfish and use Twofish with TWOFISH_SMALL defined its still 768 bytes.  Even at its largest the structure is only 
4KB which is normally not a problem for any platform.  


Cipher Name | Size of scheduled key (bytes) |
------------+-------------------------------|
Twofish     | 4,256                         |
Blowfish    | 4,168                         |
3DES        | 768                           |
SAFER+      | 532                           |
Serpent     | 528                           |
Rijndael    | 516                           |
XTEA        | 256                           |
RC2         | 256                           |
DES         | 256                           |
SAFER [#]   | 217                           |
RC5         | 204                           |
Twofish [*] | 193                           |
RC6         | 176                           |
CAST5       | 132                           |
Noekeon     | 32                            |
Skipjack    | 10                            |
------------+-------------------------------/
Memory used per cipher on a 32-bit platform.

[*] For Twofish with TWOFISH_SMALL defined
[#] For all 64-bit SAFER ciphers.

Noekeon is a fairly fast cipher and uses very little memory.  Ideally in low-ram platforms all other ciphers should be
left undefined and Noekeon should remain.  While Noekeon is generally considered a secure block cipher (it is insecure
as a hash) CAST5 is perhaps a "runner-up" choice.  CAST5 has been around longer (it is also known as CAST-128) and is 
fairly fast as well.

You can easily accomplish this via the "config.pl" script. Simply answer "n" to all of the ciphers except the one you want
and then rebuild the library.  [or you can hand edit mycrypt_custom.h]