How to Implement drdrHash Step-by-Step (With Examples)drdrHash is a hypothetical hashing algorithm used here as an example to demonstrate how to design, implement, and test a cryptographic-style hash function. This article walks through a step-by-step implementation, explains design choices, provides example code in multiple languages, shows test vectors, and discusses performance and security considerations. Note that drdrHash in this article is illustrative — do not use it in real-world cryptographic systems without thorough cryptanalysis and peer review.
Overview: goals and properties
- Purpose: educational demonstration of building a simple, deterministic hash function.
- Desired properties:
- Deterministic — same input always yields same output.
- Avalanche effect — small input changes produce significant output changes.
- Fixed-size output — produce a 256-bit (32-byte) digest.
- Fast and simple — easy to implement for learning; not intended as a secure replacement for standard hashes (SHA-256, BLAKE3, etc.).
drdrHash design (high level)
drdrHash is built from simple primitives:
- Input is processed in 64-byte (512-bit) blocks.
- A 256-bit internal state (4 × 64-bit words) is initialized with fixed constants.
- Each block is mixed into the state using bitwise operations: XOR, rotations, additions, and an S-box-like nonlinear mixing step.
- A finalization step pads the message (similar to Merkle–Damgård-style padding), processes the length, and outputs the concatenation of the state words as the digest.
Key design decisions:
- 64-bit words chosen for practical speed on modern architectures.
- Simple nonlinear mixing to encourage diffusion.
- Padding includes message length to prevent simple extension attacks in the illustrative design — but note: this alone does not guarantee resistance.
Step 1 — Message padding
We adopt a padding scheme similar to MD/SHA family:
- Append a single 0x80 byte.
- Append zero bytes until message length (mod 64) equals 56.
- Append the 64-bit big-endian message bit-length.
Example pseudocode:
function pad(message): bit_len = len(message) * 8 message += 0x80 while (len(message) % 64) != 56: message += 0x00 message += to_big_endian_64(bit_len) return message Step 2 — Initialization
Set initial state (four 64-bit words) to constants — chosen arbitrarily for illustration:
- H0 = 0x0123456789ABCDEF
- H1 = 0x0FEDCBA987654321
- H2 = 0xA5A5A5A5A5A5A5A5
- H3 = 0x5A5A5A5A5A5A5A5A
Step 3 — Compression/mix function
For each 64-byte block, split into eight 64-bit words M0..M7 (big-endian). Then perform 12 rounds of mixing:
Pseudo-operations per round (for i from 0 to 11):
- For j in 0..3: state[j] += M[(i + j) % 8] + C[i][j]
- state[0] ^= rotate_right(state[1], 29)
- state[1] = (state[1] + rotate_left(state[2], 17)) ^ SBOX(state[3])
- state[2] ^= rotate_right(state[3], 43)
- state[3] = (state[3] + rotate_left(state[0], 31)) ^ SBOX(state[1])
- Optional: swap state words in a predefined pattern.
Here C[i][j] are round constants (64-bit) derived from a sequence (e.g., fractional parts of cube roots). SBOX is a small nonlinear function; for example: SBOX(x) = ((x ^ 0xDEADBEEFDEADBEEF) * 0x9E3779B97F4A7C15) ^ ((x << 13) | (x >> (64-13)))
This mixing uses additions, rotations, XORs, and nonlinear SBOX to spread input bits.
Step 4 — Finalization
After processing all message blocks:
- XOR the message length into H3.
- Run a final 24-round mixing using zero message words but with distinct round constants to further diffuse state.
- Output digest = H0 || H1 || H2 || H3 (concatenate big-endian).
The digest is 32 bytes (256 bits).
Reference implementation — Python
Below is a clear educational Python implementation. It’s unoptimized and intended for clarity.
# drdrhash.py — educational implementation from struct import pack, unpack_from # 64-bit rotation helpers def rotl(x, n): return ((x << n) & 0xFFFFFFFFFFFFFFFF) | (x >> (64 - n)) def rotr(x, n): return (x >> n) | ((x << (64 - n)) & 0xFFFFFFFFFFFFFFFF) # S-box-like nonlinear function def sbox(x): return ((x ^ 0xDEADBEEFDEADBEEF) * 0x9E3779B97F4A7C15) ^ rotl(x, 13) # Padding def pad(message: bytes) -> bytes: bit_len = len(message) * 8 msg = bytearray(message) msg.append(0x80) while (len(msg) % 64) != 56: msg.append(0) msg += pack('>Q', bit_len) return bytes(msg) # Round constants (simple sequence for example) ROUND_CONSTS = [[(i * 0x243F6A8885A308D3) ^ (j * 0x13198A2E03707344) & 0xFFFFFFFFFFFFFFFF for j in range(4)] for i in range(24)] # Initialization IV = [ 0x0123456789ABCDEF, 0x0FEDCBA987654321, 0xA5A5A5A5A5A5A5A5, 0x5A5A5A5A5A5A5A5A ] def compress(state, block_words): state = state[:] # copy for r in range(12): # add message + round constants for j in range(4): state[j] = (state[j] + block_words[(r + j) % 8] + ROUND_CONSTS[r][j]) & 0xFFFFFFFFFFFFFFFF state[0] ^= rotr(state[1], 29) state[1] = ((state[1] + rotl(state[2], 17)) & 0xFFFFFFFFFFFFFFFF) ^ sbox(state[3]) state[2] ^= rotr(state[3], 43) state[3] = ((state[3] + rotl(state[0], 31)) & 0xFFFFFFFFFFFFFFFF) ^ sbox(state[1]) # simple permutation state[0], state[1], state[2], state[3] = state[3], state[0], state[1], state[2] return state def drdrhash(message: bytes) -> bytes: msg = pad(message) state = IV[:] for b in range(0, len(msg), 64): block = msg[b:b+64] words = [unpack_from('>Q', block, offset=i*8)[0] for i in range(8)] state = compress(state, words) # finalization state[3] ^= len(message) * 8 # extra mixing state = compress(state, [0]*8) # produce digest digest = b''.join(pack('>Q', x) for x in state[:4]) return digest # Example if __name__ == "__main__": print(drdrhash(b"").hex()) print(drdrhash(b"abc").hex()) Examples and test vectors
Run the Python script above to compute digest hex strings. Example outputs (illustrative — actual will depend on exact constants and implementation):
- drdrHash(“”) => e3b0c44298fc1c14… (example only)
- drdrHash(“abc”) => b5d4045c4d3f2a9e…
Always generate and record your own test vectors from the implementation.
C implementation (concise)
Below is a conceptual C implementation outline (not fully optimized or exhaustive error-checked):
// drdrhash.c — conceptual snippet #include <stdint.h> #include <string.h> uint64_t rotl64(uint64_t x, int n){ return (x<<n) | (x>>(64-n)); } uint64_t rotr64(uint64_t x, int n){ return (x>>n) | (x<<(64-n)); } uint64_t sbox(uint64_t x){ return ((x ^ 0xDEADBEEFDEADBEEFULL) * 0x9E3779B97F4A7C15ULL) ^ rotl64(x,13); } /* Implement pad, compress, finalization similar to Python example. */ Security considerations
- drdrHash is purely educational. Do not use drdrHash for real security. It has not undergone cryptanalysis.
- Use proven algorithms (SHA-2, SHA-3, BLAKE2/3) for production.
- Key attacks to consider: collision finding, preimage attacks, length-extension, differential cryptanalysis.
- Performance and side-channel resistance are not addressed in this example.
Performance tips
- Implement in C or Rust and use 64-bit intrinsics.
- Unroll rounds and minimize memory allocations.
- Consider using SIMD for parallel block processing if algorithm design permits.
Testing and verification
- Create test vectors for empty message, common inputs, and long random inputs.
- Use unit tests comparing your implementation in multiple languages.
- Fuzz the implementation with random inputs to find crashes or inconsistencies.
Conclusion
This article presented a step-by-step educational implementation of a simple 256-bit hash function called drdrHash. The focus was on clarity: padding, state initialization, a compression function with nonlinear mixing, finalization, and example code. Remember this is an instructional construct — rely on standardized, peer-reviewed hash functions for any security-critical work.
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