Which of the following levels of algorithms does Public Key Infrastructure (PKI) use?

PKI is fundamentally built on asymmetric (public-key) cryptography, and RSA is the predominant algorithm used for certificate-based operations such as signing and key exchange. RSA 1024-bit was the traditional baseline key length for PKI implementations, though current standards now recommend a minimum of 2048-bit due to advances in factoring attacks.

AES is a symmetric encryption algorithm and is not used for PKI's asymmetric key operations; additionally, 1024-bit is not a valid AES key size - AES is defined only for 128, 192, and 256-bit keys.

RSA 512-bit is considered cryptographically broken because it is feasible to factor a 512-bit RSA modulus with modern hardware, making it unsuitable for any PKI use.

AES is a symmetric block cipher and is architecturally incompatible with PKI's asymmetric key model; 512-bit is also not a defined AES key length.