BLAKE2s256 Security-Focused API Documentation

Version: 1.0
Last Updated: 2025-07-05
**Security Classification: PUBLIC
Author: Phantom (phantom@metamui.id)

Overview

BLAKE2s is a cryptographic hash function optimized for 8-32 bit platforms, designed as a faster alternative to SHA-256 while maintaining the same security level. BLAKE2s256 specifically produces 256-bit (32-byte) outputs and supports keyed hashing, salting, and personalization. It’s ideal for constrained environments and embedded systems.

Security Level: 256-bit (128-bit collision resistance)
Output Size: 32 bytes (256 bits)
Key Size: 0-32 bytes (optional)
Salt Size: 8 bytes (optional)
Personalization: 8 bytes (optional)

Security Warnings ⚠️

1. Not for Passwords: Use Argon2 for password hashing, not BLAKE2s
2. Key Size Limit: Keys must be ≤ 32 bytes; longer keys need pre-hashing
3. Platform Choice: Consider BLAKE2b on 64-bit systems for better performance
4. Keyed Mode: When using keys, this provides MAC functionality
5. Salt/Personalization: Are public parameters, not secret keys

API Functions

blake2s256(data: bytes, key: bytes = b"", salt: bytes = b"", person: bytes = b"") -> bytes[32]

Security Contract:

• Preconditions:
  • data can be any length
  • key must be 0-32 bytes (or pre-hash if longer)
  • salt must be 0 or 8 bytes
  • person must be 0 or 8 bytes
• Postconditions:
  • Returns exactly 32 bytes
  • Keyed mode provides MAC functionality
  • Salt/personalization provide domain separation

Attack Resistance: | Attack Type | Protected | Notes | |————-|———–|——-| | Collision | ✅ | 2^128 security (birthday bound) | | Preimage | ✅ | 2^256 security | | Second Preimage | ✅ | 2^256 security | | Length Extension | ✅ | Tree structure prevents | | Timing Attack | ✅ | Constant time implementation | | Key Recovery | ✅ | When used as MAC |

Security Requirements:

• Use random keys for MAC functionality
• Salt/personalization should be unique per domain
• Don’t truncate output without analysis
• Consider key rotation for long-term use

Secure Usage Example:

import hashlib
import hmac
import secrets
import struct
import time
from typing import Optional, Dict, List

class SecureBLAKE2s256:
    """Secure BLAKE2s256 usage patterns"""
    
    def __init__(self):
        self.hash_cache = {}
        self.key_derivation_counter = 0
        
    def simple_hash(self, data: bytes) -> bytes:
        """Simple cryptographic hash"""
        
        # Use Blake2s with no key for simple hashing
        h = hashlib.blake2s(data, digest_size=32)
        return h.digest()
    
    def keyed_hash(self, key: bytes, message: bytes) -> bytes:
        """Create MAC using BLAKE2s in keyed mode"""
        
        if len(key) > 32:
            # Pre-hash long keys
            key = hashlib.blake2s(key, digest_size=32).digest()
        elif len(key) < 16:
            raise ValueError("Key should be at least 16 bytes for security")
        
        # Use keyed mode for MAC
        h = hashlib.blake2s(
            message,
            digest_size=32,
            key=key
        )
        return h.digest()
    
    def domain_separated_hash(
        self,
        data: bytes,
        domain: str,
        context: bytes = b""
    ) -> bytes:
        """Hash with domain separation using personalization"""
        
        # Use personalization for domain separation (8 bytes max)
        person = domain.encode()[:8].ljust(8, b'\x00')
        
        # Use salt for additional context if provided
        salt = context[:8].ljust(8, b'\x00') if context else b'\x00' * 8
        
        h = hashlib.blake2s(
            data,
            digest_size=32,
            salt=salt,
            person=person
        )
        return h.digest()
    
    def derive_key(
        self,
        master_key: bytes,
        context: str,
        info: bytes = b""
    ) -> bytes:
        """Derive subkey from master key"""
        
        # Build derivation input
        derivation_input = (
            f"KeyDerivation:{context}:".encode() +
            struct.pack('<Q', self.key_derivation_counter) +
            info
        )
        
        # Derive using keyed BLAKE2s
        derived = self.keyed_hash(master_key, derivation_input)
        
        self.key_derivation_counter += 1
        return derived
    
    def create_file_integrity_hash(
        self,
        file_path: str,
        chunk_size: int = 8192
    ) -> Dict:
        """Create integrity hash for file"""
        
        import os
        
        # Get file metadata
        stat = os.stat(file_path)
        metadata = {
            'size': stat.st_size,
            'mtime': int(stat.st_mtime),
            'path': file_path
        }
        
        # Hash file content
        h = hashlib.blake2s(digest_size=32)
        
        with open(file_path, 'rb') as f:
            while chunk := f.read(chunk_size):
                h.update(chunk)
        
        content_hash = h.digest()
        
        # Hash metadata
        metadata_bytes = (
            f"File:{file_path}:Size:{metadata['size']}:MTime:{metadata['mtime']}"
        ).encode()
        
        metadata_hash = self.simple_hash(metadata_bytes)
        
        # Combine hashes
        combined_hash = self.simple_hash(content_hash + metadata_hash)
        
        return {
            'content_hash': content_hash.hex(),
            'metadata_hash': metadata_hash.hex(),
            'combined_hash': combined_hash.hex(),
            'metadata': metadata,
            'algorithm': 'BLAKE2s256'
        }

# SECURE: Message authentication with BLAKE2s
class BLAKE2s256MAC:
    def __init__(self, key: bytes):
        if len(key) < 16:
            raise ValueError("MAC key should be at least 16 bytes")
        
        # Derive MAC key to ensure proper length
        if len(key) != 32:
            self.mac_key = hashlib.blake2s(
                key,
                digest_size=32,
                person=b"MAC-Key\x00"
            ).digest()
        else:
            self.mac_key = key
    
    def create_mac(
        self,
        message: bytes,
        context: bytes = b""
    ) -> bytes:
        """Create message authentication code"""
        
        # Include context in MAC computation
        mac_input = message
        if context:
            mac_input = (
                struct.pack('<Q', len(context)) +
                context +
                struct.pack('<Q', len(message)) +
                message
            )
        
        # Compute MAC
        h = hashlib.blake2s(
            mac_input,
            digest_size=32,
            key=self.mac_key
        )
        return h.digest()
    
    def verify_mac(
        self,
        message: bytes,
        mac: bytes,
        context: bytes = b""
    ) -> bool:
        """Verify MAC with constant-time comparison"""
        
        expected = self.create_mac(message, context)
        return hmac.compare_digest(expected, mac)
    
    def create_timestamped_mac(self, message: bytes) -> Dict:
        """Create MAC with timestamp"""
        
        timestamp = int(time.time())
        timestamp_bytes = struct.pack('<Q', timestamp)
        
        # Include timestamp in MAC
        mac = self.create_mac(message + timestamp_bytes)
        
        return {
            'mac': mac.hex(),
            'timestamp': timestamp,
            'algorithm': 'BLAKE2s256-MAC'
        }

# SECURE: Tree hashing with BLAKE2s
class BLAKE2s256TreeHash:
    def __init__(self, fanout: int = 2):
        self.fanout = fanout
        
    def hash_tree(self, leaves: List[bytes]) -> bytes:
        """Compute tree hash of leaves"""
        
        if not leaves:
            return hashlib.blake2s(
                b"empty-tree",
                digest_size=32,
                person=b"TreeHash"
            ).digest()
        
        # Hash all leaves
        current_level = []
        for i, leaf in enumerate(leaves):
            # Use salt to distinguish leaf level
            leaf_hash = hashlib.blake2s(
                leaf,
                digest_size=32,
                salt=struct.pack('<Q', i)[:8],
                person=b"Leaf\x00\x00\x00\x00"
            ).digest()
            current_level.append(leaf_hash)
        
        # Build tree levels
        level = 0
        while len(current_level) > 1:
            next_level = []
            
            for i in range(0, len(current_level), self.fanout):
                # Combine up to fanout nodes
                combined = b"".join(current_level[i:i+self.fanout])
                
                # Use personalization to indicate internal node
                node_hash = hashlib.blake2s(
                    combined,
                    digest_size=32,
                    salt=struct.pack('<Q', level)[:8],
                    person=b"Internal"
                ).digest()
                next_level.append(node_hash)
            
            current_level = next_level
            level += 1
        
        return current_level[0]
    
    def verify_tree_inclusion(
        self,
        leaf: bytes,
        leaf_index: int,
        proof: List[bytes],
        root: bytes
    ) -> bool:
        """Verify leaf is included in tree"""
        
        # Start with leaf hash
        current = hashlib.blake2s(
            leaf,
            digest_size=32,
            salt=struct.pack('<Q', leaf_index)[:8],
            person=b"Leaf\x00\x00\x00\x00"
        ).digest()
        
        # Compute path to root
        index = leaf_index
        level = 0
        
        for sibling in proof:
            if index % self.fanout == 0:
                # Current is left child
                combined = current + sibling
            else:
                # Current is right child
                combined = sibling + current
            
            current = hashlib.blake2s(
                combined,
                digest_size=32,
                salt=struct.pack('<Q', level)[:8],
                person=b"Internal"
            ).digest()
            
            index //= self.fanout
            level += 1
        
        return hmac.compare_digest(current, root)

# SECURE: Commitment scheme using BLAKE2s
def create_blake2s_commitment(
    value: bytes,
    blinding_factor: Optional[bytes] = None
) -> tuple:
    """Create hiding commitment using BLAKE2s"""
    
    if blinding_factor is None:
        blinding_factor = secrets.token_bytes(32)
    
    # Commitment = BLAKE2s(blinding || value)
    commitment_input = blinding_factor + value
    commitment = hashlib.blake2s(
        commitment_input,
        digest_size=32,
        person=b"Commit\x00\x00"
    ).digest()
    
    return commitment, blinding_factor

def verify_blake2s_commitment(
    value: bytes,
    blinding_factor: bytes,
    commitment: bytes
) -> bool:
    """Verify commitment opening"""
    
    expected_commitment, _ = create_blake2s_commitment(value, blinding_factor)
    return hmac.compare_digest(expected_commitment, commitment)

Common Mistakes:

# INSECURE: Password hashing with BLAKE2s
password_hash = hashlib.blake2s(password.encode()).digest()  # Use Argon2!

# INSECURE: Weak key for MAC
mac = hashlib.blake2s(data, key=b"secret123").digest()  # Weak key!

# INSECURE: Using salt as secret
mac = hashlib.blake2s(data, salt=secret_key).digest()  # Salt is not secret!

# INSECURE: No domain separation
hash1 = blake2s256(data1)
hash2 = blake2s256(data2)  # Could collide in protocols

blake2s256_init(key: bytes = b"", salt: bytes = b"", person: bytes = b"") -> BLAKE2sContext

Security Contract:

• Preconditions:
  • Parameters same as blake2s256()
  • Creates stateful hasher object
• Postconditions:
  • Returns hasher for incremental hashing
  • Can process unlimited data
  • Thread-safe per instance

Security Notes:

• State contains key material if keyed
• Don’t serialize hasher with keys
• Each instance independent

Secure Usage Example:

use blake2::{Blake2s256, Blake2sMac};
use blake2::digest::{Digest, KeyInit, FixedOutput, Mac};
use rand::{RngCore, thread_rng};

/// Secure streaming BLAKE2s hasher
pub struct SecureBlake2sStream {
    hasher: Blake2s256,
    bytes_processed: u64,
    checkpoints: Vec<[u8; 32]>,
}

impl SecureBlake2sStream {
    pub fn new() -> Self {
        Self {
            hasher: Blake2s256::new(),
            bytes_processed: 0,
            checkpoints: Vec::new(),
        }
    }
    
    pub fn new_keyed(key: &[u8]) -> Self {
        Self {
            hasher: Blake2s256::new_with_prefix(key),
            bytes_processed: 0,
            checkpoints: Vec::new(),
        }
    }
    
    pub fn update(&mut self, data: &[u8]) -> Result<(), Error> {
        self.hasher.update(data);
        self.bytes_processed += data.len() as u64;
        
        // Create checkpoint every MB
        if self.bytes_processed % (1024 * 1024) == 0 {
            let checkpoint = self.hasher.clone().finalize().into();
            self.checkpoints.push(checkpoint);
        }
        
        Ok(())
    }
    
    pub fn finalize(self) -> HashResult {
        let final_hash = self.hasher.finalize().into();
        
        HashResult {
            hash: final_hash,
            bytes_processed: self.bytes_processed,
            checkpoints: self.checkpoints,
        }
    }
}

/// BLAKE2s for API authentication
pub struct ApiAuthenticator {
    secret_key: [u8; 32],
}

impl ApiAuthenticator {
    pub fn new() -> Self {
        let mut key = [0u8; 32];
        thread_rng().fill_bytes(&mut key);
        
        Self { secret_key: key }
    }
    
    pub fn sign_request(
        &self,
        method: &str,
        path: &str,
        body: &[u8],
        timestamp: u64,
    ) -> String {
        // Create canonical request
        let canonical = format!(
            "{}\\n{}\\n{}\\n{}",
            method,
            path,
            hex::encode(Blake2s256::digest(body)),
            timestamp
        );
        
        // Sign with BLAKE2s MAC
        let mut mac = Blake2sMac::new_from_slice(&self.secret_key)
            .expect("key size is valid");
        mac.update(canonical.as_bytes());
        
        base64::encode(mac.finalize().into_bytes())
    }
    
    pub fn verify_request(
        &self,
        method: &str,
        path: &str,
        body: &[u8],
        timestamp: u64,
        signature: &str,
    ) -> Result<(), Error> {
        // Check timestamp freshness
        let current_time = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)?
            .as_secs();
        
        if (current_time as i64 - timestamp as i64).abs() > 300 {
            return Err(Error::RequestExpired);
        }
        
        // Verify signature
        let expected = self.sign_request(method, path, body, timestamp);
        
        if !constant_time_eq(expected.as_bytes(), signature.as_bytes()) {
            return Err(Error::InvalidSignature);
        }
        
        Ok(())
    }
}

/// Secure random beacon using BLAKE2s
pub struct RandomBeacon {
    previous_output: [u8; 32],
    round_number: u64,
    secret_seed: [u8; 32],
}

impl RandomBeacon {
    pub fn new() -> Self {
        let mut seed = [0u8; 32];
        let mut initial = [0u8; 32];
        thread_rng().fill_bytes(&mut seed);
        thread_rng().fill_bytes(&mut initial);
        
        Self {
            previous_output: initial,
            round_number: 0,
            secret_seed: seed,
        }
    }
    
    pub fn next_round(&mut self, public_input: &[u8]) -> [u8; 32] {
        // Combine secret seed, public input, previous output, and round
        let mut hasher = Blake2s256::new();
        hasher.update(&self.secret_seed);
        hasher.update(public_input);
        hasher.update(&self.previous_output);
        hasher.update(&self.round_number.to_le_bytes());
        
        let output = hasher.finalize().into();
        
        // Update state
        self.previous_output = output;
        self.round_number += 1;
        
        output
    }
}

blake2s256_update(ctx: &mut BLAKE2sContext, data: bytes)

Security Contract:

• Preconditions:
  • Context not finalized
  • Can process any amount of data
• Postconditions:
  • Internal state updated
  • Order of updates matters
  • Cannot be undone

blake2s256_finalize(ctx: BLAKE2sContext) -> bytes[32]

Security Contract:

• Preconditions:
  • Context has been created
  • Can be called only once per context
• Postconditions:
  • Returns final 32-byte hash
  • Context is consumed
  • Hash includes proper padding

Security Best Practices

Embedded System Integration

class EmbeddedBLAKE2s:
    """BLAKE2s for resource-constrained environments"""
    
    def __init__(self, max_memory: int = 1024):
        self.max_memory = max_memory  # bytes
        self.chunk_size = min(256, max_memory // 4)
        
    def hash_large_data(
        self,
        data_source,
        total_size: int
    ) -> bytes:
        """Hash large data with memory constraints"""
        
        h = hashlib.blake2s(digest_size=32)
        processed = 0
        
        while processed < total_size:
            # Read chunk that fits in memory
            chunk_size = min(self.chunk_size, total_size - processed)
            chunk = data_source.read(chunk_size)
            
            if not chunk:
                break
            
            h.update(chunk)
            processed += len(chunk)
        
        return h.digest()
    
    def incremental_mac(
        self,
        key: bytes,
        data_chunks: list
    ) -> bytes:
        """Compute MAC incrementally"""
        
        if len(key) > 32:
            key = hashlib.blake2s(key, digest_size=32).digest()
        
        h = hashlib.blake2s(digest_size=32, key=key)
        
        for chunk in data_chunks:
            h.update(chunk)
        
        return h.digest()

IoT Device Authentication

/// BLAKE2s for IoT device authentication
pub struct IoTDeviceAuth {
    device_id: [u8; 16],
    device_key: [u8; 32],
    sequence_number: u64,
}

impl IoTDeviceAuth {
    pub fn new(device_id: [u8; 16], device_key: [u8; 32]) -> Self {
        Self {
            device_id,
            device_key,
            sequence_number: 0,
        }
    }
    
    pub fn create_authenticated_message(
        &mut self,
        payload: &[u8],
    ) -> Vec<u8> {
        // Message format: device_id + sequence + payload + mac
        
        let mut message = Vec::new();
        message.extend_from_slice(&self.device_id);
        message.extend_from_slice(&self.sequence_number.to_le_bytes());
        message.extend_from_slice(payload);
        
        // Compute MAC over header + payload
        let mut mac = Blake2sMac::new_from_slice(&self.device_key)
            .expect("key size is valid");
        mac.update(&message);
        let auth_tag = mac.finalize().into_bytes();
        
        // Append MAC
        message.extend_from_slice(&auth_tag);
        
        self.sequence_number += 1;
        
        message
    }
    
    pub fn verify_message(
        &self,
        message: &[u8],
    ) -> Result<(u64, Vec<u8>), Error> {
        if message.len() < 16 + 8 + 32 {  // min size
            return Err(Error::MessageTooShort);
        }
        
        // Extract components
        let device_id = &message[..16];
        let sequence = u64::from_le_bytes(message[16..24].try_into().unwrap());
        let payload_end = message.len() - 32;
        let payload = &message[24..payload_end];
        let received_mac = &message[payload_end..];
        
        // Verify device ID
        if device_id != self.device_id {
            return Err(Error::InvalidDeviceId);
        }
        
        // Verify MAC
        let mut mac = Blake2sMac::new_from_slice(&self.device_key)
            .expect("key size is valid");
        mac.update(&message[..payload_end]);
        
        if mac.verify_slice(received_mac).is_err() {
            return Err(Error::AuthenticationFailed);
        }
        
        Ok((sequence, payload.to_vec()))
    }
}

Blockchain Integration

class BLAKE2sBlockchain:
    """BLAKE2s for lightweight blockchain"""
    
    def __init__(self, chain_id: str):
        self.chain_id = chain_id.encode()[:8].ljust(8, b'\x00')
        
    def hash_block(self, block_data: dict) -> bytes:
        """Hash block with chain-specific personalization"""
        
        # Serialize block data
        import json
        block_bytes = json.dumps(block_data, sort_keys=True).encode()
        
        # Hash with chain personalization
        return hashlib.blake2s(
            block_bytes,
            digest_size=32,
            person=self.chain_id
        ).digest()
    
    def hash_transaction(self, tx_data: dict) -> bytes:
        """Hash transaction"""
        
        import json
        tx_bytes = json.dumps(tx_data, sort_keys=True).encode()
        
        return hashlib.blake2s(
            tx_bytes,
            digest_size=32,
            salt=b"TX\x00\x00\x00\x00\x00\x00"
        ).digest()
    
    def create_merkle_root(self, tx_hashes: List[bytes]) -> bytes:
        """Create Merkle root of transactions"""
        
        tree = BLAKE2s256TreeHash(fanout=2)
        return tree.hash_tree(tx_hashes)

Common Integration Patterns

Distributed Hash Table

def consistent_hash_blake2s(key: str, num_buckets: int) -> int:
    """Consistent hashing using BLAKE2s"""
    
    # Hash key to get uniform distribution
    hash_bytes = hashlib.blake2s(
        key.encode(),
        digest_size=32,
        person=b"DHT-Hash"
    ).digest()
    
    # Convert to integer and map to bucket
    hash_int = int.from_bytes(hash_bytes, 'big')
    return hash_int % num_buckets

Firmware Verification

/// Firmware verification using BLAKE2s
pub fn verify_firmware_signature(
    firmware_data: &[u8],
    expected_hash: &[u8; 32],
    device_key: &[u8; 32],
) -> Result<(), Error> {
    // Hash firmware with device-specific key
    let mut mac = Blake2sMac::new_from_slice(device_key)
        .expect("key size is valid");
    mac.update(b"FIRMWARE-v1:");
    mac.update(firmware_data);
    
    let computed_hash = mac.finalize().into_bytes();
    
    if !constant_time_eq(&computed_hash, expected_hash) {
        return Err(Error::FirmwareVerificationFailed);
    }
    
    Ok(())
}

Performance Considerations

Platform	BLAKE2s Speed	SHA-256 Speed	Advantage
ARM Cortex-M4	12.5 cycles/byte	22 cycles/byte	1.8x faster
AVR 8-bit	850 cycles/byte	1400 cycles/byte	1.6x faster
RISC-V 32-bit	15 cycles/byte	28 cycles/byte	1.9x faster
ESP32	8.2 cycles/byte	14 cycles/byte	1.7x faster

Optimization Tips

• Use BLAKE2sp for parallel processing
• Pre-compute personalization/salt
• Batch multiple hash operations
• Consider BLAKE2b on 64-bit embedded systems

Security Auditing

Verification Checklist

• Not using for password hashing directly
• Key size ≤ 32 bytes (or pre-hashed)
• Salt/personalization used correctly
• Constant-time comparison for MACs
• Domain separation implemented
• Memory usage within constraints

Common Vulnerabilities

# AUDIT: Look for these patterns

# ❌ Password hashing
blake2s256(password)  # Use Argon2!

# ❌ Short keys for MAC
blake2s256(data, key=b"1234")  # Too short!

# ❌ Salt used as key
blake2s256(data, salt=secret)  # Salt is public!

# ❌ No domain separation
# Multiple protocols using same parameters

# ❌ Memory exhaustion
# Processing gigabytes on microcontroller

Security Analysis

Threat Model: BLAKE2s Threat Model

The comprehensive threat analysis covers:

• Algorithm-specific attack vectors
• Implementation vulnerabilities
• Side-channel considerations
• Quantum resistance analysis (where applicable)
• Deployment recommendations

For complete security analysis and risk assessment, see the dedicated threat model documentation.

References

1. RFC 7693 - BLAKE2 Cryptographic Hash and MAC
2. BLAKE2 Paper
3. BLAKE2 Website

Support

Security Issues: security@metamui.id
Documentation Updates: phantom@metamui.id
Vulnerability Disclosure: See SECURITY.md

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Document Version: 1.0
Review Cycle: Quarterly
Next Review: 2025-04-05
Classification: PUBLIC