Message Level Encryption (MLE) is required for use of Cardholder Database Update API and Card Services API. Issuers that opt for the full service API model where cryptographic information is forwarded in the API message will be required to use MLE in the outbound API message. For the lite model, where Visa does on-behalf-of validation on all cryptographic information, MLE is not required for outbound API messages. MLE provides an enhanced security for message payload by using asymmetric encryption technique (public-key cryptography). You can generate the encryption/decryption key pairs in the Sandbox, Certification, or Production environments. For details, refer to the Message Level Encryption Documentation.