SHA-256
SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function that produces a fixed 256-bit (32-byte) digest from any input, making it computationally infeasible to modify a document without changing its hash.
What it means
When a document is signed, the signing software computes the SHA-256 hash of the document content and signs that hash with the signer's private key. Any subsequent modification to even a single byte of the document produces a completely different hash, immediately revealing tampering. SHA-256 is the current industry standard, replacing the deprecated SHA-1.
Why it matters for e-signatures
Every document signed through SignOwl has its SHA-256 hash computed and embedded in the signature. This is the mathematical guarantee that what you signed is exactly what the recipient received — unchanged.
Related terms
Frequently asked questions
Can SHA-256 be reversed to recover the original document?
No. SHA-256 is a one-way function. You can verify a document matches its hash, but you cannot reconstruct the document from the hash alone.
Why was SHA-1 deprecated in favor of SHA-256?
Researchers demonstrated practical collision attacks against SHA-1 in 2017 (the SHAttered attack), meaning two different documents could be crafted to produce the same hash. SHA-256 has no known collision vulnerabilities.
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