How does digital document signing work?

Digital document signing uses cryptographic methods to ensure both the integrity of the document and the identity of the signer:

Signing Request: The signer is prompted to sign the document. This can be done through various software or platforms specialized in digital signatures. For example, DocuSeal is a free and open-source tool for signing PDF documents.

Identity Verification: The signer’s identity is verified, often using a digital certificate issued by a trusted Certificate Authority (CA). This certificate uniquely identifies the signer.

Signature Creation: When the signer agrees to sign, the digital signing software generates a unique data block or “hash” of the document. The signer’s private key, which is securely stored and accessible only to the signer, encrypts this hash. This encrypted hash, along with the signer’s digital certificate, forms the digital signature.

Document Sealing: The digital signature is then attached to the document. Once signed, the document is ‘sealed’, and any subsequent changes to the document can be detected.

Verification by Recipients: Any recipient of the signed document can verify the signature. This is done by decrypting the hash with the signer’s public key, which is available in the signer’s digital certificate. The recipient’s software generates a new hash of the received document and compares it with the decrypted hash. If they match, it confirms that the document has not been altered since signing and that the signature is valid.

Integrity and Non-repudiation: The cryptographic nature of the signature ensures that the document has not been altered post-signing, and the signer cannot deny signing the document.

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