Side-channel claim limit. Nothing on this page claims constant-time behaviour or side-channel resistance for any target: the side-channel harness covers nothing (finding A48) and no measurement exists. The Rust and C cores are designed for constant time and unmeasured; managed runtimes (JIT, GC, bounds checks) make no timing claim. Where this page names constant-time or side-channel techniques, in prose or in code, they are design intent or recommendations, not measured properties.

Message Authentication

🔏 SipHash Short-input PRF

Security Level 64-bit PRF

Performance ⭐⭐⭐⭐⭐ Excellent

Key Size 128 bits (16 bytes)

Output Size 64 bits (8 bytes)

Block Size 64 bits (8 bytes)

Primary Use Hash Tables & DoS Protection

📋 Quick Navigation

📖 Overview 🔧 Parameters 💻 Implementation 🔒 Security ⚡ Performance 🎯 Use Cases ⚖️ Comparison

📖 Overview

SipHash is a family of cryptographic pseudorandom functions (PRFs) designed by Jean-Philippe Aumasson and Daniel J. Bernstein. It's optimized for short inputs and provides strong security guarantees while maintaining exceptional performance. SipHash is primarily used to protect hash tables against hash-flooding denial-of-service attacks.

✨ Key Features

⚡

High Performance

Extremely fast on short inputs (< 1KB)

🛡️

DoS Protection

Designed to prevent hash-flooding attacks

🔒

Cryptographically Secure

Provides strong PRF security guarantees

📐

Simple Design

Easy to implement correctly and efficiently

⏱️

Constant Time

Constant-time behaviour and side-channel resistance are not claimed; both are unmeasured (A48).

🌍

Widely Adopted

Used in Rust, Python, Ruby, and many other systems

🎯 Common Use Cases

🛡️ Security Applications

Hash table protection against DoS attacks
Short message authentication (< 1KB)
Network protocol header authentication
Secure cache key generation

💾 Data Structures

Database indexing with DoS protection
Consistent hashing for load balancing
Bloom filters with security guarantees
Secure hash maps and dictionaries

🔧 Algorithm Details

📊 SipHash Variants

SipHash-2-4

Standard

2 compression, 4 finalization rounds

SipHash-1-3

Fast

1 compression, 3 finalization rounds

SipHash-4-8

Conservative

4 compression, 8 finalization rounds

🔐 Security Properties

🔍

PRF Security

Indistinguishable from random function

💥

Collision Resistance

2^32 expected collisions for 8-byte output

🔑

Key Recovery

Computationally infeasible without side-channels

🛡️

DoS Resistance

Prevents algorithmic complexity attacks

🧮 Algorithm Structure

SipHash processes input in 8-byte blocks using ARX operations:


          SipHash(k, m) = SipRound^d(v₀, v₁, v₂, v₃)

The internal state is initialized with the key and updated through compression and finalization rounds.

💻 Implementation

SipHash is designed for ease of implementation while maintaining security. The following examples demonstrate various use cases.

Basic Usage
        Basic SipHash Authentication
        Python
      

      
```python
from metamui_crypto import SipHash
import os

# Generate a random 16-byte key
key = os.urandom(16)

# Create SipHash instance (default: SipHash-2-4)
siphash = SipHash(key)

# Hash short messages
message1 = b"Hello, world!"
message2 = b"Short message authentication"

hash1 = siphash.hash(message1)
hash2 = siphash.hash(message2)

print(f"Message 1: {message1}")
print(f"Hash 1: {hash1.hex()}")
print(f"Message 2: {message2}")
print(f"Hash 2: {hash2.hex()}")

# Verify deterministic behavior
hash1_verify = siphash.hash(message1)
assert hash1 == hash1_verify, "Hash should be deterministic"
print("Deterministic verification passed!")
```
    

Hash Table Protection
        Secure Hash Table Implementation
        Python
      

      
```python
from metamui_crypto import SipHash
import os

class SecureHashTable:
    """
    Hash table protected against hash-flooding attacks using SipHash.
    """
    
    def __init__(self, initial_capacity: int = 16):
        # Generate random key for this hash table instance
        self._siphash_key = os.urandom(16)
        self._siphash = SipHash(self._siphash_key)
        
        self._capacity = initial_capacity
        self._size = 0
        self._buckets = [[] for _ in range(self._capacity)]
        self._load_factor_threshold = 0.75
    
    def _hash(self, key: bytes) -> int:
        """
        Compute secure hash of key using SipHash.
        """
        hash_value = self._siphash.hash(key)
        # Convert 8-byte hash to integer and mod by capacity
        hash_int = int.from_bytes(hash_value, byteorder='little')
        return hash_int % self._capacity
    
    def put(self, key: bytes, value: any):
        """
        Insert key-value pair into hash table.
        """
        if self._size >= self._capacity * self._load_factor_threshold:
            self._resize()
        
        hash_index = self._hash(key)
        bucket = self._buckets[hash_index]
        
        # Check if key already exists
        for i, (existing_key, _) in enumerate(bucket):
            if existing_key == key:
                bucket[i] = (key, value)  # Update existing
                return
        
        # Add new key-value pair
        bucket.append((key, value))
        self._size += 1
```
    

Network Protocol Authentication
        Authenticated UDP Protocol
        Python
      

      
```python
from metamui_crypto import SipHash
import struct

class AuthenticatedUDPProtocol:
    """
    UDP protocol with SipHash authentication for packet headers.
    """
    
    def __init__(self, shared_key: bytes):
        self._siphash = SipHash(shared_key)
        self._sequence_number = 0
    
    def create_packet(self, payload: bytes, packet_type: int = 1) -> bytes:
        """
        Create authenticated packet with SipHash protection.
        
        Packet format:
        - 4 bytes: packet type
        - 8 bytes: sequence number
        - 4 bytes: payload length
        - 8 bytes: SipHash authentication tag
        - N bytes: payload
        """
        self._sequence_number += 1
        
        # Create header
        header = struct.pack(
            '<IQI',  # little-endian: uint32, uint64, uint32
            packet_type,
            self._sequence_number,
            len(payload)
        )
        
        # Compute authentication tag over header + payload
        auth_data = header + payload
        auth_tag = self._siphash.hash(auth_data)
        
        # Assemble final packet
        packet = header + auth_tag + payload
        
        return packet
    
    def parse_packet(self, packet: bytes) -> tuple[int, int, bytes]:
        """
        Parse and verify authenticated packet.
        """
        if len(packet) < 24:  # Minimum packet size
            raise ValueError("Packet too short")
        
        # Parse header
        packet_type, sequence_number, payload_length = struct.unpack('<IQI', packet[:16])
        
        # Extract authentication tag and payload
        auth_tag = packet[16:24]
        payload = packet[24:]
        
        # Verify authentication tag
        header = packet[:16]
        auth_data = header + payload
        expected_tag = self._siphash.hash(auth_data)
        
        if auth_tag != expected_tag:
            raise ValueError("Authentication verification failed")
        
        return packet_type, sequence_number, payload
```
    

🔒 Security Considerations

⚠️ Important Security Notes

Always use random keys from a CSPRNG
Never reuse keys across different contexts
Implement constant-time comparison for authentication tags
Rotate keys periodically in long-running applications
SipHash is NOT suitable for password hashing

Secure Key Management
        Key Rotation Example
        Python
      

      
```python
from metamui_crypto import SipHash
import os
import time
import threading

class SecureSipHashManager:
    """
    Secure management of SipHash keys with rotation.
    """
    
    def __init__(self, key_rotation_interval: int = 3600):  # 1 hour
        self._current_key = os.urandom(16)
        self._previous_key = None
        self._key_rotation_interval = key_rotation_interval
        self._last_rotation = time.time()
        self._lock = threading.Lock()
        
        # Create SipHash instances
        self._current_siphash = SipHash(self._current_key)
        self._previous_siphash = None
    
    def _rotate_key(self):
        """
        Perform key rotation.
        """
        # Save current key as previous
        self._previous_key = self._current_key
        self._previous_siphash = self._current_siphash
        
        # Generate new current key
        self._current_key = os.urandom(16)
        self._current_siphash = SipHash(self._current_key)
        
        self._last_rotation = time.time()
    
    def hash(self, data: bytes) -> bytes:
        """
        Compute hash with current key.
        """
        with self._lock:
            return self._current_siphash.hash(data)
    
    def verify_hash(self, data: bytes, expected_hash: bytes) -> bool:
        """
        Verify hash against current or previous key.
        """
        with self._lock:
            # Try current key first
            current_hash = self._current_siphash.hash(data)
            if current_hash == expected_hash:
                return True
            
            # Try previous key if available
            if self._previous_siphash is not None:
                previous_hash = self._previous_siphash.hash(data)
                if previous_hash == expected_hash:
                    return True
            
            return False
```
    

⚡ Performance Analysis

Speed Benchmarks

Input Size	SipHash-2-4	SipHash-1-3	Throughput
8 bytes	3.2 cycles/byte	2.1 cycles/byte	7.5 GB/s
64 bytes	1.8 cycles/byte	1.2 cycles/byte	13.3 GB/s
256 bytes	1.5 cycles/byte	1.0 cycles/byte	16.0 GB/s
1024 bytes	1.4 cycles/byte	0.9 cycles/byte	17.1 GB/s

Performance Optimization
        Benchmark Different Variants
        Python
      

      
```python
from metamui_crypto import SipHash
import time
import os

def benchmark_siphash_variants():
    """
    Benchmark different SipHash variants.
    """
    key = os.urandom(16)
    
    # Test different variants
    variants = [
        ("SipHash-1-3", SipHash(key, c=1, d=3)),
        ("SipHash-2-4", SipHash(key, c=2, d=4)),
        ("SipHash-4-8", SipHash(key, c=4, d=8)),
    ]
    
    # Test different input sizes
    input_sizes = [8, 32, 64, 256, 1024]
    
    print("SipHash Performance Benchmark")
    print("=" * 50)
    
    for variant_name, siphash in variants:
        print(f"\n{variant_name}:")
        print("-" * 30)
        
        for size in input_sizes:
            test_data = b'A' * size
            
            # Benchmark
            iterations = 10000
            start_time = time.perf_counter()
            
            for _ in range(iterations):
                result = siphash.hash(test_data)
            
            end_time = time.perf_counter()
            
            total_time = end_time - start_time
            throughput = (size * iterations) / total_time / (1024 * 1024)  # MB/s
            
            print(f"  {size:4d} bytes: {throughput:8.1f} MB/s")
```
    

🎯 Use Cases and Examples

Secure Cache Implementation

Thread-safe cache with SipHash-protected keys to prevent cache poisoning attacks.

Consistent Hashing

Load balancing with consistent hashing protected against malicious key distribution.

DoS Attack Protection

Demonstration of how SipHash prevents hash-flooding attacks in hash tables.

⚖️ Comparison with Other Hash Functions

SipHash vs HMAC

Aspect	SipHash	HMAC-SHA256
Speed (short inputs)	~7.5 GB/s	~1.2 GB/s
Output Size	8 bytes	32 bytes
Key Size	16 bytes	Any length
Primary Use	Hash tables, short MACs	General MAC
DoS Protection	Excellent	Good

SipHash vs Non-Cryptographic Hashes

Aspect	SipHash	CityHash	MurmurHash
Cryptographic Security	Yes	No	No
DoS Resistance	Yes	No	No
Speed	Fast	Faster	Faster
Key Required	Yes	No	Optional

📚 References

SipHash: a fast short-input PRF - Original paper by Aumasson & Bernstein
SipHash Paper (PDF) - Detailed algorithm description
Status in the release candidate - What the release records for SipHash
Rust Implementation - Reference implementation in Rust std