_________ is a protocol developed by Visa and MasterCard to protect electronic transactions.

SSL (Secure Sockets Layer) is a general cryptographic protocol for securing network communications, not specifically developed by Visa and MasterCard for transactions.

SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function used for data integrity, not a transaction protocol.

HMAC (Hash-based Message Authentication Code) is a mechanism for message authentication, not a comprehensive electronic transaction protocol.

SET (Secure Electronic Transaction) was a protocol jointly developed by Visa, MasterCard, and others to ensure secure credit card payments over open networks like the internet, providing confidentiality, integrity, and authentication.

ETP (Electronic Transactions Protocol) is not a widely recognized or specific protocol developed by Visa and MasterCard for this purpose.