[openssl-users] base64 decode in C
dthompson at prinpay.com
Wed Mar 18 11:34:41 UTC 2015
> From: openssl-users On Behalf Of Prashant Bapat
> Sent: Wednesday, March 18, 2015 03:37
> I'm trying to use the base64 decode function in C. <snip>
> This works well for simple b64 encoded strings like "hello world!" etc.
> But when I want to b64 decode the contents of a SSH public key, it fails. Returns nothing.
It returns pointer to a buffer containing the pubkey, but no indication of
the length. You don't show the caller, but if the caller tries to treat it as a
C string with strlen()fputs() etc that won't work because it isn't a C string.
A C string can't contain any zero-bits aka null byte, and SSH pubkey contains
many of them; it even starts with *three* consecutive nulls, which
makes it appear to be empty if treated as a C string.
Use the length returned from (successful) BIO_read (b64bio,...).
> This decodes fine.
> "dGhpcyBpcyBhd2Vzb21lCg==" : "this is awesome"
Actually that decodes as "this is awesome" PLUS A NEWLINE, or in
C source notation "this is awesome\n". Yes that matters.
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