Constant-Time bin2hex() implementation

[sarciszewski]

Contant time bin2hex() implementation, taken from jedisct1/libsodium@814df1e

[laruence]

hmm... did you ever try to make after your fix?

 hex[i * 2U] = (char) (87 + b + (((b - 10) >> 31) & -39));

where is hex's definition?

and since hexconvtab not used anymore, the definition of it should also be removed.

thanks

[sarciszewski]

How does this look now? :)

[nikic]

Can you provide information as to how this performs compared to the previous implementation? I'm not fully convinced that PHP has need for a constant time bin2hex implementation.

[sarciszewski]

I'm not fully convinced that PHP has need for a constant time bin2hex implementation.

Do PHP developers use bin2hex() (or base64_encode()) on cryptographic secrets for the purpose of storing in configuration files (.ini, .json, .yaml, or .conf.php)? If so, then PHP has a need for constant time implementations of these functions.

http://tonyarcieri.com/cream-the-scary-ssl-attack-youve-probably-never-heard-of
http://cr.yp.to/antiforgery/cachetiming-20050414.pdf

(Spoiler: Yes, we do use these features to encode cryptographic secrets. So I would argue that they are a good enhancement to include in PHP 7)

[smalyshev]

I think this needs some discussion on internals. If we worry about such things just replacing random functions is not enough - you should be sure all functions that handle your secret are constant-time, including the engine primitives, etc. I'm not sure just having one function does anything. But maybe I'm missing something here.

[sarciszewski]

If we worry about such things just replacing random functions is not enough - you should be sure all functions that handle your secret are constant-time, including the engine primitives, etc.

This is just a start. I'd love to discuss it with "internals", but my only exposure to PHP's core dev is through github.

[laruence]

@sarciszewski you can drop a mail to internals at lists.php.net :)

[nikic]

@sarciszewski It must be added to the function entry list: https://github.com/sarciszewski/php-src/blob/patch-1/ext/standard/basic_functions.c#L2664.

[sarciszewski]

Ah, thank you.

[sarciszewski]

Ugh, this got messy. Time to start over.