Hash

Abstract

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• Hash means Chop & Mix
• Take in a variable-length text and give a fixed-length output
• Same input → Same output
• Infeasible to reverse from the hash value to the original text
• We want the algorithm to have Avalanche effect (雪崩效应) and be Collision resistance (抗碰撞性)

Use Cases

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• Store secrete data in plaintext in the hash form (e.g Password)

Cons

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• Can be hacked by Rainbow Attack, Try generate a hash of common text & reverse it with this website - can be avoided using Salting

Code Examples

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Nodejs

const { createHash } = require('crypto')
 
function hash(input) {
  return createHash('sha256').update(input).digest("hex")
}
 
let password = 'password123'
console.log(hash(password));

Terminologies

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MD5 (Message Digest)

• A Hashing Algorithm that can be broken

SHA256 (Secure Hash Algorithm)

• A Hashing Algorithm that produces a fix length of Digest that is 256-bits

# Output is hex encoded
shasum -a 256 <FILE_NAME>

Digest

• A hash value that is commonly formatted as hex or Base 64 Encoding