Crate base64ct[−][src]
Expand description
RustCrypto: Constant-Time Base64
Pure Rust implementation of Base64 (RFC 4648).
Implements multiple Base64 variants without data-dependent branches or lookup tables, thereby providing portable “best effort” constant-time operation.
Supports no_std
environments and avoids heap allocations in the core API
(but also provides optional alloc
support for convenience).
About
This crate implements several Base64 variants in constant-time for sidechannel resistance, aimed at purposes like encoding/decoding the “PEM” format used to store things like cryptographic private keys.
The paper Util::Lookup: Exploiting key decoding in cryptographic libraries demonstrates how the leakage from non-constant-time Base64 parsers can be used to practically extract RSA private keys from SGX enclaves.
The padded variants require (=
) padding. Unpadded variants expressly
reject such padding.
Whitespace is expressly disallowed.
Supported Base64 variants
- Standard Base64:
[A-Z]
,[a-z]
,[0-9]
,+
,/
- URL-safe Base64:
[A-Z]
,[a-z]
,[0-9]
,-
,_
- bcrypt Base64:
.
,/
,[A-Z]
,[a-z]
,[0-9]
crypt(3)
Base64:.
,-
,[0-9]
,[A-Z]
,[a-z]
Minimum Supported Rust Version
This crate requires Rust 1.56 at a minimum.
We may change the MSRV in the future, but it will be accompanied by a minor version bump.
License
Licensed under either of:
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
Usage
Allocating (enable alloc
crate feature)
use base64ct::{Base64, Encoding};
let bytes = b"example bytestring!";
let encoded = Base64::encode_string(bytes);
assert_eq!(encoded, "ZXhhbXBsZSBieXRlc3RyaW5nIQ==");
let decoded = Base64::decode_vec(&encoded).unwrap();
assert_eq!(decoded, bytes);
Heapless no_std
usage
use base64ct::{Base64, Encoding};
const BUF_SIZE: usize = 128;
let bytes = b"example bytestring!";
assert!(Base64::encoded_len(bytes) <= BUF_SIZE);
let mut enc_buf = [0u8; BUF_SIZE];
let encoded = Base64::encode(bytes, &mut enc_buf).unwrap();
assert_eq!(encoded, "ZXhhbXBsZSBieXRlc3RyaW5nIQ==");
let mut dec_buf = [0u8; BUF_SIZE];
let decoded = Base64::decode(encoded, &mut dec_buf).unwrap();
assert_eq!(decoded, bytes);
Implementation
Implemented using bitwise arithmetic alone without any lookup tables or data-dependent branches, thereby providing portable “best effort” constant-time operation.
Not constant-time with respect to message length (only data).
Adapted from the following constant-time C++ implementation of Base64:
https://github.com/Sc00bz/ConstTimeEncoding/blob/master/base64.cpp
Copyright (c) 2014 Steve “Sc00bz” Thomas (steve at tobtu dot com). Derived code is dual licensed MIT + Apache 2 (with permission from Sc00bz).
Structs
Standard Base64 encoding with =
padding.
bcrypt Base64 encoding.
crypt(3)
Base64 encoding.
Standard Base64 encoding without padding.
URL-safe Base64 encoding with =
padding.
URL-safe Base64 encoding without padding.
Stateful Base64 decoder with support for buffered, incremental decoding.
Invalid encoding of provided Base64 string.
Insufficient output buffer length.
Enums
Generic error, union of InvalidLengthError
and InvalidEncodingError
.
Traits
Base64 encoding trait.