Add a glossary page on digital signatures

files/en-us/glossary/digital_signature/index.md

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+---
+title: Digital signature
+slug: Glossary/Digital_signature
+page-type: glossary-definition
+---
+
+{{GlossarySidebar}}
+
+A **digital signature** is an object that can be used to {{glossary("authentication", "authenticate")}} the author of a document or message.
+
+Digital signatures are usually based on {{glossary("public-key cryptography")}}, in which a key is created as a pair of keys, with the property that if some input is encrypted with one key, it can only be decrypted with the other key, and vice versa.
+
+The creator of the key pair then makes one of the keys public and keeps the other one private. To sign a document, the key pair's owner creates a {{glossary("hash")}} of the document and encrypts it with the private key.
+
+They send the document and the signature to the verifier, who hashes the document, then retrieves the public key and decrypts the signature: if this matches the hash then the signature has been verified, and the verifier can be confident that the signature was created by an entity with access to the private key.
+
+The security of a digital signature system depends (among other things) on:
+
+- The private key's owner keeping it safe: if other entities can access the private key, they can impersonate the owner.
+
+- The public key used by the verifier being the genuine counterpart of the owner's private key: if an attacker could trick the verifier into trusting the wrong public key, they could impersonate the owner.
+
+Verifiers often use {{glossary("digital certificate", "digital certificates")}} to check that public keys are genuine.
+
+## See also
+
+- {{glossary("Digital certificate")}}
+- {{glossary("Hash")}}
+- {{glossary("Public-key cryptography")}}