Struct password_hash::Salt
source · [−]pub struct Salt<'a>(_);
Expand description
Salt string.
In password hashing, a “salt” is an additional value used to personalize/tweak the output of a password hashing function for a given input password.
Salts help defend against attacks based on precomputed tables of hashed passwords, i.e. “rainbow tables”.
The Salt
type implements the RECOMMENDED best practices for salts
described in the PHC string format specification, namely:
- Maximum lengths for salt, output and parameter values are meant to help consumer implementations, in particular written in C and using stack-allocated buffers. These buffers must account for the worst case, i.e. the maximum defined length. Therefore, keep these lengths low.
- The role of salts is to achieve uniqueness. A random salt is fine for that as long as its length is sufficient; a 16-byte salt would work well (by definition, UUID are very good salts, and they encode over exactly 16 bytes). 16 bytes encode as 22 characters in B64. Functions should disallow salt values that are too small for security (4 bytes should be viewed as an absolute minimum).
Recommended length
The recommended default length for a salt string is 16-bytes (128-bits).
See Salt::RECOMMENDED_LENGTH
for more information.
Constraints
Salt strings are constrained to the following set of characters per the PHC spec:
The salt consists in a sequence of characters in:
[a-zA-Z0-9/+.-]
(lowercase letters, uppercase letters, digits, /, +, . and -).
Additionally the following length restrictions are enforced based on the guidelines from the spec:
- Minimum length: 4-bytes
- Maximum length: 64-bytes
A maximum length is enforced based on the above recommendation for supporting stack-allocated buffers (which this library uses), and the specific determination of 64-bytes is taken as a best practice from the Argon2 Encoding specification in the same document:
The length in bytes of the salt is between 8 and 64 bytes†, thus yielding a length in characters between 11 and 64 characters (and that length is never equal to 1 modulo 4). The default byte length of the salt is 16 bytes (22 characters in B64 encoding). An encoded UUID, or a sequence of 16 bytes produced with a cryptographically strong PRNG, are appropriate salt values.
†The Argon2 specification states that the salt can be much longer, up to 2^32-1 bytes, but this makes little sense for password hashing. Specifying a relatively small maximum length allows for parsing with a stack allocated buffer.)
Based on this guidance, this type enforces an upper bound of 64-bytes as a reasonable maximum, and recommends using 16-bytes.
Implementations
sourceimpl<'a> Salt<'a>
impl<'a> Salt<'a>
sourcepub const MIN_LENGTH: usize = 4usize
pub const MIN_LENGTH: usize = 4usize
Minimum length of a Salt
string: 4-bytes.
sourcepub const MAX_LENGTH: usize = 64usize
pub const MAX_LENGTH: usize = 64usize
sourcepub const RECOMMENDED_LENGTH: usize = 16usize
pub const RECOMMENDED_LENGTH: usize = 16usize
Recommended length of a salt: 16-bytes.
This recommendation comes from the PHC string format specification:
The role of salts is to achieve uniqueness. A random salt is fine for that as long as its length is sufficient; a 16-byte salt would work well (by definition, UUID are very good salts, and they encode over exactly 16 bytes). 16 bytes encode as 22 characters in B64.
sourcepub fn new(input: &'a str) -> Result<Self>
pub fn new(input: &'a str) -> Result<Self>
Create a Salt
from the given str
, validating it according to
Salt::MIN_LENGTH
and Salt::MAX_LENGTH
length restrictions.
sourcepub fn b64_decode<'b>(&self, buf: &'b mut [u8]) -> Result<&'b [u8]>
pub fn b64_decode<'b>(&self, buf: &'b mut [u8]) -> Result<&'b [u8]>
Attempt to decode a B64-encoded Salt
, writing the decoded result
into the provided buffer, and returning a slice of the buffer
containing the decoded result on success.
Trait Implementations
sourceimpl<'a> From<&'a SaltString> for Salt<'a>
impl<'a> From<&'a SaltString> for Salt<'a>
sourcefn from(salt_string: &'a SaltString) -> Salt<'a>
fn from(salt_string: &'a SaltString) -> Salt<'a>
Converts to this type from the input type.
impl<'a> Copy for Salt<'a>
impl<'a> Eq for Salt<'a>
impl<'a> StructuralEq for Salt<'a>
impl<'a> StructuralPartialEq for Salt<'a>
Auto Trait Implementations
impl<'a> RefUnwindSafe for Salt<'a>
impl<'a> Send for Salt<'a>
impl<'a> Sync for Salt<'a>
impl<'a> Unpin for Salt<'a>
impl<'a> UnwindSafe for Salt<'a>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more