Proposal Details

Background

The current implementations of the base32 and base64 codecs are not ideal for cryptographic use cases. The linked document describes practical timing side-channels against general purpose RFC 4648 codecs when used to encode/decode cryptographic secrets. You can verify the current implementation uses a table look-up in both directions, which introduces the risk of cache-timing attacks.

Specialized implementations of these codecs exist. @Sc00bz wrote a constant-time implementation of base64 in C, which I used as a basis for both base32 and base64 in PHP.

Proposed Change

New functions in encoding/base32 and encoding/base64:

• EncodeToStringConstTime as an alternative to EncodeToString
• DecodeStringConstTime as an alternative to DecodeString

These functions could then be used in other packages that handle cryptographic secrets and auditors can be absolutely sure that timing leaks are not present.

(I'm happy to provide a patch for this, if accepted.)