Legal Definitions - hash number

A hash number (sometimes called a hashed number or message digest) is a unique, fixed-length string of characters, typically numerical, that is generated from a digital file or message using a specific mathematical algorithm. It acts like a digital fingerprint for the data: even a tiny change to the original data will produce a completely different hash number. In legal and digital security contexts, hash numbers are crucial for verifying the integrity and authenticity of digital information, especially when creating a digital signature.

• Digital Contract Signing

  Scenario: A real estate agent sends a purchase agreement to a client to sign electronically. Before the client signs, a unique hash number is calculated for that specific version of the contract document.

  Illustration: When the client applies their digital signature, this hash number is encrypted using the client's private key. This process creates a digital signature that is inextricably linked to that exact version of the contract. If even a single word in the contract were changed after signing, the hash number would be different, and the digital signature would no longer be valid, proving the document's integrity has been compromised.

• Verifying Digital Evidence in Court

  Scenario: A cybersecurity expert collects a copy of a computer's hard drive as evidence in a fraud case. Immediately after creating the copy, they generate a hash number for the entire digital image of the hard drive.

  Illustration: This hash number serves as a tamper-proof identifier. If the digital evidence is later presented in court, a new hash number can be generated from the evidence and compared to the original. If the hash numbers match, it provides strong assurance that the digital evidence has not been altered or corrupted since it was first collected, maintaining its integrity for legal proceedings.

• Secure Transmission of Confidential Documents

  Scenario: A law firm needs to send a highly confidential legal brief to a client via an online portal. To ensure the client receives the exact, unaltered document, the firm's system calculates a hash number for the brief before uploading it.

  Illustration: This hash number is then digitally signed by the law firm and sent along with the brief. When the client downloads the brief, their system can calculate its own hash number for the received document. If this newly calculated hash number matches the one embedded in the law firm's digital signature, the client can be confident that the brief they received is authentic and has not been tampered with during transmission.