Which encryption standard has been identified by NIST to be replaced by AES due to security issues?

The encryption standard identified by NIST to be replaced by AES due to security vulnerabilities is 3DES (Triple Data Encryption Standard). 3DES was designed to provide a more robust encryption method by applying the older DES (Data Encryption Standard) algorithm three times to each data block, effectively increasing the key length and security. However, as computational power increased and cryptographic analysis improved, vulnerabilities were discovered in 3DES.

Among these vulnerabilities are issues such as its vulnerability to meet modern security requirements, including increased key length, and efficient attack methods that have surfaced over the years. While 3DES was an improvement over DES, it is now considered inadequate for protecting sensitive data against contemporary threats, which is why NIST recommended transitioning to AES (Advanced Encryption Standard) as a more secure alternative. AES not only provides stronger encryption with larger key sizes but also supports more efficient algorithms that are better suited for modern computing environments.

The other options listed, such as OFB, CTR, and CBC, represent modes of operation for block ciphers rather than encryption standards themselves, which is not applicable to the context of being replaced due to security vulnerabilities.