S/MIME (Secure/Multipurpose Internet Mail Extensions) protocol implements the Rivest-Shamir-Adleman (RSA) encryption algorithm for digital signatures in emails. Digital signatures are a key component of S/MIME, providing authentication, message integrity, and non-repudiation. RSA is a widely used public-key cryptosystem that facilitates secure data transmission and is known for its role in digital signatures. It works on the principle of asymmetric cryptography, where a pair of keys is used: a public key, which is shared openly, and a private key, which is kept secret by the owner. In the context of S/MIME, the sender's email client uses the sender's private key to create a digital signature, and the recipient's email client uses the sender's public key to verify the signature.
References: The information provided is based on the S/MIME protocol's use of RSA encryption for digital signatures, as detailed in industry-standard documentation and resources like Microsoft Learn1 and the S/MIME Wikipedia page2.