Which of the following encryption encoding techniques is used in the basic authentication method?

In HTTP Basic Authentication, the client concatenates the username and password with a colon (username:password) and encodes the result using Base64, then sends it in the Authorization header. Base64 is a binary-to-text encoding scheme, not a cryptographic operation, meaning the credentials are trivially reversible. This is why Basic Authentication must always be used over HTTPS to provide actual confidentiality.

DES in ECB mode is a symmetric block cipher used for encryption, not the encoding mechanism employed by HTTP Basic Authentication.

HMAC-MD5 is a keyed hash function used for message integrity and authentication, not for encoding credentials in Basic Auth headers.

MD5 is a one-way cryptographic hash function and cannot be used as a reversible encoding scheme, so it is not used in Basic Authentication.