Crate base64ct

source ·
Expand description

Pure Rust implementation of Base64 encoding (RFC 4648, section 4) with a constant-time no_std-friendly implementation.


This crate implements several Base64 variants in constant-time.

The padded variants require (=) padding. Unpadded variants expressly reject such padding.

Whitespace is expressly disallowed.

Minimum Supported Rust Version

This crate requires Rust 1.47 at a minimum.

We may change the MSRV in the future, but it will be accompanied by a minor version bump.


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);


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:

Copyright (c) 2014 Steve “Sc00bz” Thomas (steve at tobtu dot com). Derived code is dual licensed MIT + Apache 2 (with permission from Sc00bz).


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.
Invalid encoding of provided Base64 string.
Insufficient output buffer length.


Generic error, union of InvalidLengthError and InvalidEncodingError.


Base64 encoding trait.