add a convenient way for common pbkdf2::<Hmac<Sha1>>(*** )

[sxci]

eg:

let mut bytes = [0u8; 16];
pbkdf2::<Hmac<Sha1>>(password, b"saltysalt", 1003, bytes.as_mut());

go lang : https://pkg.go.dev/golang.org/x/crypto/pbkdf2

dk := pbkdf2.Key([]byte(password), []byte("saltysalt"), 1003, 16, sha1.New)

in rust, there are additional info: mut bytes , Hmac,
golang's pbkdf2.Key look like more convenient

[newpavlov]

It comes to different philosophies between Rust and Go. Go is quite happy to use dynamic dispatch and heap allocated data, while in Rust we prefer monomorphization and stack-based structures. Note that PBKDF2 is defined in terms of a keyed PRF, HMAC is just one example of such function. For example, BLAKE2 functions can be used as such function directly without HMAC.

I guess we could introduce something like this to save on Hmac import:

type pbkdf2_hmac<T> = pbkdf2<Hmac<T>>;

It also would allow users to remove the hmac crate from their Cargo.toml.

But I think we will leave everything else as-is.

P.S.: While we are comparing conveniences, Go's []byte(..) looks terrible to me.

[tarcieri]

@newpavlov perhaps an allocating API like pbkdf2_vec which accepts an output length argument ala Go would be a useful addition?

[newpavlov]

@tarcieri
I don't think we should introduce allocating methods without a good reason. A better option would be to introduce a const generic based API which returns an array with generated key. The current API was developed long before const generics were stabilized.