Legal Definitions - hash

"Hashing" refers to the process of applying a specific mathematical function, known as a hashing algorithm, to a piece of digital data, such as a document, file, or message. This process generates a unique, fixed-length string of characters, often called a "hash value" or "digest." Even a tiny change to the original data will result in a completely different hash value. The primary purposes of hashing are to ensure the integrity of data (confirming it hasn't been altered) and to create digital signatures (verifying the origin and integrity of a document).

• Software Integrity Verification:

  Imagine a software company releases a critical security update for its operating system. To help users verify that their downloaded file is legitimate and hasn't been corrupted or tampered with by malicious actors during transit, the company publishes a unique hash value (e.g., SHA-256) for the update file on its website.

  How it illustrates "hashing": After downloading the update, a user can run a hashing tool on the downloaded file on their own computer. If the hash value calculated by the user's tool matches the one provided by the software company, it confirms that the downloaded file is an exact, unaltered copy of the original file released by the vendor. This ensures the integrity of the software before installation.

• Legal Document Archiving:

  A law firm finalizes a crucial settlement agreement with a client and opposing counsel. They want to ensure that this specific version of the digital document (a PDF) remains immutable and verifiable for many years, preventing any future disputes about its content.

  How it illustrates "hashing": Before archiving the final PDF, the firm can "hash" the document using a robust algorithm. The resulting unique hash value is then recorded and stored separately in a secure, tamper-proof ledger or database. If, at a later date, there is any question about the contract's authenticity or whether it has been modified, the firm can re-hash the archived PDF. If the newly generated hash value matches the original stored hash, it provides strong evidence that the document's contents have remained unchanged since it was first hashed and archived.

• Digital Signatures for Contracts:

  A business executive needs to digitally sign an important contract with a vendor, ensuring the vendor knows the contract originated from her and that its contents haven't been altered after her approval.

  How it illustrates "hashing": Instead of a physical signature, the executive's computer system first "hashes" the entire contract document. This creates a unique digital fingerprint of the document. This hash value is then encrypted using the executive's private digital key, creating the digital signature. Both the contract and the digital signature are then sent to the vendor. When the vendor receives the contract, their system can use the executive's publicly available digital key to decrypt the signature, revealing the original hash value. Simultaneously, their system will independently hash the received contract document. If the hash value derived from the document matches the hash value recovered from the digital signature, it confirms both that the contract has not been tampered with since the executive signed it (integrity) and that it genuinely originated from the executive (authentication).