UUID v5 Generator

What is UUID Version 5?

UUID version 5 is a name-based, deterministic UUID generated by hashing a namespace identifier together with a name using the SHA-1 algorithm. The key property of UUID v5 is that given the same namespace and name, you will always get the exact same UUID.

This makes UUID v5 fundamentally different from UUID v4 (random) or UUID v1 (timestamp-based). Instead of generating a new unique identifier each time, UUID v5 creates a consistent identifier that can be reproduced anywhere, anytime, as long as you know the inputs.

UUID v5 is defined in RFC 4122 Section 4.3 and is preferred over UUID v3 (which uses MD5) because SHA-1 is a stronger hash function.

How UUID v5 Generation Works

UUID v5 is generated through the following process:

1. 1 Concatenate the namespace UUID (16 bytes) with the name (UTF-8 encoded)
2. 2 Compute SHA-1 hash of the concatenated data (produces 20 bytes)
3. 3 Take the first 16 bytes of the hash
4. 4 Set version bits to "0101" (5) in the 7th byte
5. 5 Set variant bits to "10" in the 9th byte

Standard Namespaces

RFC 4122 defines four standard namespace UUIDs for common use cases:

UUID v5 vs UUID v3

Both UUID v3 and v5 are name-based and deterministic. The only difference is the hash algorithm:

Note: While SHA-1 itself has theoretical weaknesses for cryptographic signatures, it remains perfectly adequate for UUID generation where collision resistance (not pre-image resistance) is the primary concern.

When to Use UUID v5

Generate UUID v5 in Code

import uuid

# Using standard DNS namespace
dns_namespace = uuid.NAMESPACE_DNS
uuid_v5 = uuid.uuid5(dns_namespace, "example.com")
print(uuid_v5)  # cfbff0d1-9375-5685-968c-48ce8b15ae17

# Using URL namespace
url_namespace = uuid.NAMESPACE_URL
uuid_v5 = uuid.uuid5(url_namespace, "https://example.com/page")

# Custom namespace (your own application)
my_namespace = uuid.UUID("12345678-1234-5678-1234-567812345678")
uuid_v5 = uuid.uuid5(my_namespace, "[email protected]")

import { v5 as uuidv5 } from 'uuid';

// Standard namespaces
const DNS_NAMESPACE = '6ba7b810-9dad-11d1-80b4-00c04fd430c8';
const URL_NAMESPACE = '6ba7b811-9dad-11d1-80b4-00c04fd430c8';

// Generate UUID v5
const id = uuidv5('example.com', DNS_NAMESPACE);
console.log(id);  // cfbff0d1-9375-5685-968c-48ce8b15ae17

// Same inputs always produce same output
console.log(uuidv5('example.com', DNS_NAMESPACE) === id);  // true

import java.util.UUID;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;

// Java doesn't have built-in v5, but you can implement it:
public static UUID generateUUIDv5(UUID namespace, String name) {
    MessageDigest md = MessageDigest.getInstance("SHA-1");
    md.update(toBytes(namespace));
    md.update(name.getBytes(StandardCharsets.UTF_8));
    byte[] hash = md.digest();
    
    hash[6] = (byte) ((hash[6] & 0x0f) | 0x50);  // version 5
    hash[8] = (byte) ((hash[8] & 0x3f) | 0x80);  // variant
    
    return fromBytes(hash);
}

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