crypto-async-rs 0.1.3

//! # HKDF (HMAC-based Key Derivation Function)
//!
//! This module provides HKDF implementation for key derivation as specified in RFC 5869.
//! HKDF is a simple key derivation function that can be used to derive one or more
//! cryptographically strong secret keys from some source of initial keying material.
//!
//! ## Features
//!
//! - RFC 5869 compliant HKDF implementation
//! - Two-step process: Extract and Expand
//! - Support for arbitrary output lengths
//! - Uses HMAC-SHA256 as the underlying hash function
//!
//! ## Example
//!
//! ```rust
//! use crypto_async_rs::hkdf;
//!
//! let salt = b"random-salt";
//! let ikm = b"input-key-material";
//! let info = b"application-info";
//!
//! // Extract phase - derive a pseudorandom key
//! let prk = hkdf::extract_sha256(salt, ikm);
//!
//! // Expand phase - derive multiple keys
//! let encryption_key = hkdf::expand_sha256(&prk, b"encryption", 32);
//! let mac_key = hkdf::expand_sha256(&prk, b"mac", 32);
//! ```

use crate::hmac;

/// Extract a fixed-length pseudorandom key from input keying material
///
/// This is the first phase of HKDF. It takes some source of initial keying material
/// and derives from it a fixed-length pseudorandom key.
///
/// # Arguments
/// * `salt` - Optional salt value (can be empty)
/// * `ikm` - Input keying material
///
/// # Returns
/// A 32-byte pseudorandom key
///
/// # Example
/// ```rust
/// use crypto_async_rs::hkdf;
///
/// let salt = b"random-salt";
/// let ikm = b"input-key-material";
/// let prk = hkdf::extract_sha256(salt, ikm);
/// ```
pub fn extract_sha256(salt: &[u8], ikm: &[u8]) -> [u8; 32] {
    hmac::hmac_sha256(salt, ikm)
}

/// Generic extract function for use with different HMAC implementations
pub fn extract<T: AsRef<[u8]>>(salt: &[u8], ikm: &[u8], hmac: fn(&[u8], &[u8]) -> T) -> T {
    hmac(salt, ikm)
}

/// Expand a pseudorandom key into additional pseudorandom keys
///
/// This is the second phase of HKDF. It expands the pseudorandom key into
/// one or more additional pseudorandom keys of arbitrary length.
///
/// # Arguments
/// * `prk` - Pseudorandom key (usually from extract phase)
/// * `info` - Optional context and application specific information
/// * `l` - Desired output length in bytes
///
/// # Returns
/// A boxed slice containing the derived key material
///
/// # Example
/// ```rust
/// use crypto_async_rs::hkdf;
///
/// let prk = [0u8; 32]; // Pseudorandom key from extract phase
/// let info = b"encryption-key";
/// let key = hkdf::expand_sha256(&prk, info, 32);
/// ```
pub fn expand_sha256(prk: &[u8], info: &[u8], l: usize) -> Box<[u8]> {
    //    let n = ((l / 32) as f32).ceil() as usize;
    let mut result: Vec<u8> = Vec::with_capacity(l);
    let text_max_len = 32 + info.len() + 1;

    let mut t: Vec<u8> = Vec::with_capacity(text_max_len);
    let mut i = 0usize;
    while result.len() < l {
        t.extend_from_slice(info);
        i += 1;
        t.push(i as u8);
        let hmac_hash = hmac::hmac_sha256(prk, &t);
        t.truncate(0);
        t.extend_from_slice(&hmac_hash);
        result.extend_from_slice(&hmac_hash);
    }

    result.truncate(l);
    result.into_boxed_slice()
}

pub fn expand<T: AsRef<[u8]>>(
    prk: &[u8],
    info: &[u8],
    l: usize,
    hmac: fn(&[u8], &[u8]) -> T,
) -> Box<[u8]> {
    //    let n = ((l / 32) as f32).ceil() as usize;
    let mut result: Vec<u8> = Vec::with_capacity(l);
    let text_max_len = 64 + info.len() + 1;

    let mut t: Vec<u8> = Vec::with_capacity(text_max_len);
    let mut i = 0usize;
    while result.len() < l {
        t.extend_from_slice(info);
        i += 1;
        t.push(i as u8);
        let hmac_hash = hmac(prk, &t);
        t.truncate(0);
        t.extend_from_slice(&hmac_hash.as_ref());
        result.extend_from_slice(&hmac_hash.as_ref());
    }

    result.truncate(l);
    result.into_boxed_slice()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::hmac::hmac_sha256;

    #[test]
    fn test_extract_expand_sha256_1() {
        //(80 octets)
        let ikm: [u8; 80] = [
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
            0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b,
            0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29,
            0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
            0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45,
            0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
        ];
        //(80 octets)
        let salt: [u8; 80] = [
            0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
            0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b,
            0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
            0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
            0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5,
            0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
        ];

        let info: [u8; 80] = [
            0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd,
            0xbe, 0xbf, 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb,
            0xcc, 0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9,
            0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
            0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5,
            0xf6, 0xf7, 0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
        ];

        let l = 82usize;

        let prk: [u8; 32] = [
            0x06, 0xa6, 0xb8, 0x8c, 0x58, 0x53, 0x36, 0x1a, 0x06, 0x10, 0x4c, 0x9c, 0xeb, 0x35,
            0xb4, 0x5c, 0xef, 0x76, 0x00, 0x14, 0x90, 0x46, 0x71, 0x01, 0x4a, 0x19, 0x3f, 0x40,
            0xc1, 0x5f, 0xc2, 0x44,
        ];

        let okm: [u8; 82] = [
            0xb1, 0x1e, 0x39, 0x8d, 0xc8, 0x03, 0x27, 0xa1, 0xc8, 0xe7, 0xf7, 0x8c, 0x59, 0x6a,
            0x49, 0x34, 0x4f, 0x01, 0x2e, 0xda, 0x2d, 0x4e, 0xfa, 0xd8, 0xa0, 0x50, 0xcc, 0x4c,
            0x19, 0xaf, 0xa9, 0x7c, 0x59, 0x04, 0x5a, 0x99, 0xca, 0xc7, 0x82, 0x72, 0x71, 0xcb,
            0x41, 0xc6, 0x5e, 0x59, 0x0e, 0x09, 0xda, 0x32, 0x75, 0x60, 0x0c, 0x2f, 0x09, 0xb8,
            0x36, 0x77, 0x93, 0xa9, 0xac, 0xa3, 0xdb, 0x71, 0xcc, 0x30, 0xc5, 0x81, 0x79, 0xec,
            0x3e, 0x87, 0xc1, 0x4c, 0x01, 0xd5, 0xc1, 0xf3, 0x43, 0x4f, 0x1d, 0x87,
        ];

        let result = extract(&salt, &ikm, hmac_sha256);
        assert_eq!(result, prk);

        let result: &[u8] = &expand(&prk, &info, l, hmac_sha256);
        assert_eq!(result.len(), l);
        assert_eq!(result, &okm[..]);
    }

    #[test]
    fn test_extract_expand_sha256_2() {
        let ikm: [u8; 22] = [
            0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
            0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
        ];
        //(80 octets)
        let salt: [u8; 13] = [
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,
        ];

        let info: [u8; 10] = [0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9];

        let l = 42usize;

        let prk: [u8; 32] = [
            0x07, 0x77, 0x09, 0x36, 0x2c, 0x2e, 0x32, 0xdf, 0x0d, 0xdc, 0x3f, 0x0d, 0xc4, 0x7b,
            0xba, 0x63, 0x90, 0xb6, 0xc7, 0x3b, 0xb5, 0x0f, 0x9c, 0x31, 0x22, 0xec, 0x84, 0x4a,
            0xd7, 0xc2, 0xb3, 0xe5,
        ];

        let okm: [u8; 42] = [
            0x3c, 0xb2, 0x5f, 0x25, 0xfa, 0xac, 0xd5, 0x7a, 0x90, 0x43, 0x4f, 0x64, 0xd0, 0x36,
            0x2f, 0x2a, 0x2d, 0x2d, 0x0a, 0x90, 0xcf, 0x1a, 0x5a, 0x4c, 0x5d, 0xb0, 0x2d, 0x56,
            0xec, 0xc4, 0xc5, 0xbf, 0x34, 0x00, 0x72, 0x08, 0xd5, 0xb8, 0x87, 0x18, 0x58, 0x65,
        ];

        let result = extract(&salt, &ikm, hmac_sha256);
        assert_eq!(result, prk);

        let result: &[u8] = &expand(&prk, &info, l, hmac_sha256);
        assert_eq!(result.len(), l);
        assert_eq!(result, &okm[..]);
    }

    #[test]
    fn test_extract_expand_sha256_3() {
        let ikm: [u8; 22] = [
            0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
            0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b, 0x0b,
        ];
        let l = 42usize;

        let prk: [u8; 32] = [
            0x19, 0xef, 0x24, 0xa3, 0x2c, 0x71, 0x7b, 0x16, 0x7f, 0x33, 0xa9, 0x1d, 0x6f, 0x64,
            0x8b, 0xdf, 0x96, 0x59, 0x67, 0x76, 0xaf, 0xdb, 0x63, 0x77, 0xac, 0x43, 0x4c, 0x1c,
            0x29, 0x3c, 0xcb, 0x04,
        ];

        let okm: [u8; 42] = [
            0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f, 0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c,
            0x5a, 0x31, 0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e, 0xc3, 0x45, 0x4e, 0x5f,
            0x3c, 0x73, 0x8d, 0x2d, 0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a, 0x96, 0xc8,
        ];

        let result = extract(&[], &ikm, hmac_sha256);
        assert_eq!(result, prk);

        let result: &[u8] = &expand(&prk, &[], l, hmac_sha256);
        assert_eq!(result.len(), l);
        assert_eq!(result, &okm[..]);
    }
}