The ElGamal encryption system is an asymmetric public-key cryptosystem based on the computational difficulty of the discrete logarithm problem. Its design is a direct extension of the Diffie-Hellman key exchange protocol, adapting the key agreement mechanism for encryption. In ElGamal, a sender uses the recipient's public key to generate a shared secret key for one-time use, which is then used to encrypt the plaintext. This direct lineage from the principles of Diffie-Hellman distinguishes it from other common asymmetric algorithms like RSA, which is based on the difficulty of integer factorization.

1. Elgamal, T. (1985). A public key cryptosystem and a signature scheme based on discrete logarithms. IEEE Transactions on Information Theory, 31(4), 469–472. The paper's abstract states the system is "based on the discrete logarithm problem," the same mathematical foundation as Diffie-Hellman. DOI: https://doi.org/10.1109/TIT.1985.1057074

2. Katz, J., & Lindell, Y. (2014). Introduction to Modern Cryptography (2nd ed.). CRC Press. In Chapter 11, Section 11.3, "The El Gamal Encryption Scheme," the text explicitly states, "The El Gamal encryption scheme...is closely related to the Diffie-Hellman key-exchange protocol...".

3. Rivest, R. L. (2017). Lecture 10: Public-Key Cryptography: Diffie-Hellman, ElGamal, RSA. MIT OpenCourseWare, 6.857 Computer and Network Security, Fall 2017. The lecture notes describe the ElGamal encryption scheme as being "based on Diffie-Hellman key exchange."

4. Menezes, A. J., van Oorschot, P. C., & Vanstone, S. A. (1996). Handbook of Applied Cryptography. CRC Press. In Chapter 8, Section 8.4, "ElGamal public-key encryption" (page 294), the algorithm is presented, and its relationship to the discrete logarithm problem and Diffie-Hellman is established.