GC and security

[Fredrik Lundh]

Les Schaffer wrote:

> i am working on a python application that uses encryption as part of its
> security features. so then at some point someone has to enter a
> passphrase into the system and passed into a decryption functions (we
> are using gpg via subprocess).
> 
> so i am curious. so long as i drop all reference to the passphrase
> string(s), eventually it gets garbage collected and the memory recycled.
> so "before long" the phrase is gone from memory.

Since Python uses reference counting, if you drop all references, the 
object is garbaged collected immediately, and the associated memory is 
freed.  However, freeing memory doesn't mean that the memory is cleared, 
so the passphrase will still be visible in memory, until some other part 
of your program allocates the same memory area and overwrites it.

you could obscure things a bit by storing the passphrase as a list of 
characters, or a list of integers, and write it to gpg one character at 
a time (if that's possible; if not, you may need to write a custom 
extension that builds a command string in a C-level buffer, runs the 
command, and then overwrites the buffer before returning).

</F>