In today's information age, cryptography plays a crucial role for safeguarding information security. This article will introduce common concepts of cryptography and delve into its role in securing information security from multiple dimensions.

The eavesdropping, tampering, and forgery of information by attackers pose threats to the confidentiality, integrity, authentication, and non-repudiation of information systems. Confidentiality ensures that information is not read or accessed by unauthorized entities. Integrity ensures that information is not tampered with or destroyed during transmission. Authentication ensures the authenticity of the source and recipient of the information. Non-repudiation is the ability to ensure that neither the sender nor the receiver of information can deny the information they have sent or received.

In order to achieve confidentiality, integrity, authentication, and non-repudiation in information systems, different cryptographic techniques need to be utilized. For example, “confidentiality properties” are achieved through secure communication systems, while “integrity properties” are achieved through digital signature systems.

The secure communication system consists of plaintext, ciphertext, encryption algorithm, decryption algorithm, and key. Plaintext refers to unencrypted information, while ciphertext refers to information that has been encrypted. Encryption is the process of converting plaintext into ciphertext, while decryption is the process of restoring ciphertext to plaintext. The key is critical for controlling the transformation between plaintext and ciphertext, and is divided into encryption keys and decryption keys.

Digital signature system is composed of several elements, including:

• Message: the information to be sent

• Signature Value: the value of the message after being signed with a private key

• Private Key: used for signing

• Public Key: used for verification

• Signature Algorithm: the process of signing the message

• Verification Algorithm: the process of verifying the signature value

The security of a cryptosystem depends on the key, which requires the participation of random numbers for generation. Random numbers are divided into true random numbers and pseudo-random numbers, of which pseudo-random numbers are further divided into strong pseudo-random numbers and weak pseudo-random numbers. The random numbers we use in cryptography are true random numbers and strong pseudo-random numbers. True random numbers are generated through physical phenomena, such as the noise of electronic components. Strong pseudo-random numbers are unpredictable random numbers generated through algorithms and seeds, such as using the unidirectionality of one-way hash functions to ensure the unpredictability of the pseudo-random generator.