# CSH-256: Custom Secure Hash - 256 bit

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[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
[![Python 3.8+](https://img.shields.io/badge/python-3.8+-blue.svg)](https://www.python.org/downloads/)

A hybrid password hashing algorithm combining the structural robustness of traditional cryptographic hash functions with the time-cost resistance of key derivation functions.

## Features

- 🔒 **Hardware-Resistant**: Designed to resist GPU/ASIC attacks through computational slowdown
- 🎯 **Avalanche Effect**: 51.56% bit diffusion rate (near-optimal 50%)
- ⚡ **High-Performance C Core**: Optional C extension for maximum speed
- 🔧 **Configurable**: Adjustable iteration count for future-proof security
- 🛡️ **Battle-Tested Primitives**: Uses SHA-256 structure, AES S-Box, and RSA-inspired operations
- 📦 **Zero Dependencies**: Pure Python + optional C extension

## Algorithm Overview

CSH-256 implements three security layers:

1. **Non-Linearity Layer**: AES S-Box substitution for enhanced diffusion
2. **Computational Slowdown**: Modular Cubing (h³ mod 2⁶⁴)
3. **Time-Cost Iteration**: Password stretching through repeated compression

The algorithm achieves **51.56% avalanche effect**, meaning changing a single input bit changes approximately half of the output bits.

## Installation

### From PyPI (Recommended)

```bash
pip install csh256
```

### From Source (with C extension)

```bash
git clone https://github.com/hemaabokila/CSH-256-Repo.git
cd CSH-256-Repo
pip install -e .
```

### Pure Python (no C compiler needed)

```bash
pip install csh256 --no-binary csh256
```

## Quick Start

### Basic Usage

```python
import csh256

# Hash a password (auto-generates salt)
hash_result = csh256.hash("my_secure_password")
print(hash_result)
# Output: 'a3f2b1c4d5e6f7a8b9c0d1e2f3a4b5c6...'
```

### Complete Example with Storage

```python
import csh256

# Create a hash with all parameters
result = csh256.hash_full("my_secure_password")

# Store in database (PHC format)
db.store_user(username="alice", password_hash=result['formatted'])
# Stores: '$csh256$i=4096$3f4e2a1b...$a3f2b1c4...'

# Later, verify password
stored_hash = db.get_password_hash("alice")
is_valid = csh256.verify("my_secure_password", formatted=stored_hash)
print(f"Password valid: {is_valid}")
```

### Custom Parameters

```python
import csh256

# Use custom salt and iterations
custom_salt = csh256.generate_salt()
result = csh256.hash_full(
    "my_password",
    salt=custom_salt,
    iterations=8192  # Higher = more secure but slower
)

print(f"Hash: {result['hash']}")
print(f"Salt: {result['salt'].hex()}")
print(f"Iterations: {result['iterations']}")
```

## API Reference

### Core Functions

#### `hash(password, salt=None, iterations=None)`
Generate a CSH-256 hash (returns hex string only).

**Parameters:**
- `password` (str | bytes): Password to hash
- `salt` (bytes, optional): 16-byte salt (auto-generated if None)
- `iterations` (int, optional): Iteration count (default: 4096)

**Returns:** 64-character hexadecimal hash string

---

#### `hash_full(password, salt=None, iterations=None)`
Generate complete hash with all parameters.

**Returns:** Dictionary with keys:
- `hash`: Hex hash string
- `salt`: Salt bytes
- `iterations`: Iteration count
- `formatted`: PHC-formatted string

---

#### `verify(password, hash_value=None, salt=None, iterations=None, formatted=None)`
Verify a password against stored hash.

**Parameters:**
- `password` (str | bytes): Password to verify
- Either:
  - `hash_value`, `salt`, `iterations`: Individual components
  - `formatted`: PHC-formatted string

**Returns:** `True` if valid, `False` otherwise

---

### Utility Functions

#### `generate_salt(size=16)`
Generate cryptographically secure random salt.

#### `format_hash(hash_value, salt, iterations)`
Format components into PHC string.

#### `parse_hash(formatted)`
Parse PHC string into components.

#### `recommend_iterations(target_time_ms=250)`
Recommend iteration count based on target computation time.

```python
# Find iterations for ~500ms computation
iterations = csh256.recommend_iterations(500)
print(f"Use {iterations} iterations")
```

## Performance Benchmarks

Tested on Intel i7-10700K @ 3.80GHz:

| Iterations | Time (Python) | Time (C) | Speedup |
|-----------|---------------|----------|---------|
| 1,024     | 0.85s         | 0.12s    | 7.1x    |
| 4,096     | 3.42s         | 0.48s    | 7.1x    |
| 8,192     | 6.84s         | 0.96s    | 7.1x    |
| 16,384    | 13.68s        | 1.92s    | 7.1x    |

## Security Considerations

### Recommended Iterations

- **Minimum**: 4,096 iterations
- **Standard**: 8,192 iterations (~500ms)
- **High-Security**: 16,384+ iterations (~1s+)

### Salt Requirements

- Must be **exactly 16 bytes**
- Must be **cryptographically random**
- Must be **unique per password**
- Use `csh256.generate_salt()` for secure generation

### Storage Format

Always store using PHC format:
```
$csh256$i=4096$<salt_hex>$<hash_hex>
```

This format includes all parameters needed for verification.

## Algorithm Specification

### Architecture
- **Structure**: Merkle–Damgård construction
- **Block Size**: 512 bits
- **Output Size**: 256 bits
- **Rounds**: 64 per compression

### Security Primitives
1. **SHA-256 Functions**: Σ₀, Σ₁, σ₀, σ₁, CH, MAJ
2. **AES S-Box**: 8-bit non-linear substitution
3. **RSA Primitive**: Modular Cubing (h³ mod 2⁶⁴)

### Avalanche Effect
- **Measured**: 51.56% bit diffusion
- **Ideal**: 50.00%
- **Interpretation**: Near-perfect statistical independence

## Testing

```bash
# Run all tests
pytest tests/

# Run with coverage
pytest --cov=csh256 tests/

# Run benchmarks
pytest tests/test_performance.py -v
```

## Development

```bash
# Install development dependencies
pip install -e ".[dev]"

# Format code
black csh256/ tests/

# Type checking
mypy csh256/

# Linting
flake8 csh256/
```

## Comparison with Other Algorithms

| Algorithm | Type | Memory-Hard | GPU-Resistant | Configurable Cost |
|-----------|------|-------------|---------------|-------------------|
| **CSH-256** | Hybrid | No | Yes | Yes (iterations) |
| Bcrypt | KDF | No | Partial | Yes (cost factor) |
| Scrypt | KDF | Yes | Yes | Yes (N, r, p) |
| Argon2 | KDF | Yes | Yes | Yes (t, m, p) |
| PBKDF2 | KDF | No | No | Yes (iterations) |

CSH-256 focuses on computational cost through non-parallelizable operations rather than memory hardness.

## License

MIT License - see [LICENSE](LICENSE) file for details.

## Citation

If you use CSH-256 in academic work, please cite:

```bibtex
@software{csh256,
  author = {Aboukila, Ibrahim Hilal},
  title = {CSH-256: A Hybrid Password Hashing Algorithm},
  year = {2025},
  url = {https://github.com/hemaabokila/CSH-256-Repo}
}
```

## Contributing

Contributions welcome! Please read [CONTRIBUTING.md](CONTRIBUTING.md) first.

## References

1. Rivest, R. L., et al. (1978). "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems"
2. NIST FIPS 180-4: Secure Hash Standard (SHS)
3. Daemen, J., & Rijmen, V. (2002). "The Design of Rijndael: AES"

## Author

**Ibrahim Hilal Aboukila**

## Acknowledgments

Special thanks to the cryptography community for their foundational work in hash functions and key derivation.

---

⚠️ **Security Notice**: While CSH-256 implements multiple security layers, always use the latest recommended iteration counts and follow secure password practices. For production use, conduct thorough security audits.