SHA-256

SHA-256 (Secure Hash Algorithm 256-bit) is part of the SHA-2 family designed by the NSA. It has two critical properties for document signing:

1. **Deterministic:** The same input always produces the same 256-bit hash. 2. **Avalanche effect:** Changing a single bit of the input produces a completely different hash.

In e-signatures, the entire document content (including the certificate page itself) is hashed using SHA-256. This hash is included in the certificate. Anyone can verify the document's integrity by re-hashing the content and comparing it to the stored hash.

SHA-256 is computationally infeasible to reverse — there is no known way to derive the original document from its hash, or to create a different document that produces the same hash.