Question

Briefly argue why it is untrue to say that public-key encryption is more secure than conventional encryption.

Answer 1

Dear seeker,

First I Wanted to make you aware about public key encryption

Answer to your question is simple

Any encryption scheme can be insecure if the key space is small enough.

For example, you could perform encryption with an 8 bit RSA key. For a key of that size, it's trivial to determine the private key given the public key.

Public key encryption is a form of encryption that uses two keys. A public key, which everyone knows, and a private key, which only you know. To encrypt, the public key is applied to the target information, using a predefined operation (several times), to produce a pseudo-random number. To decrypt, the private key is applied to the pseudo-random number, using a different predefined operation (several times), to get the target information back. The algorithm relies on the fact that encryption is easy, and decryption is hard, making decryption impractical without the key. It was the first system to allow secure information transfer, without a shared key.

When the two parties communicate to each other to transfer the intelligible or sensible message, referred to as plaintext, is converted into apparently random nonsense for security purpose referred to as ciphertext.
The process of changing the plaintext into the ciphertext is referred to as encryption.
The encryption process consists of an algorithm and a key. The key is a value independent of the plaintext.
Once the ciphertext is produced, it may be transmitted.
The security of conventional encryption depends on the major two factors:

The Encryption algorithm
Secrecy of the key

The algorithm will produce a different output depending on the specific key being used at the time. Changing the key changes the output of the algorithm.
Once the ciphertext is produced, it may be transmitted. Upon reception, the ciphertext can be transformed back to the original plaintext by using a decryption algorithm and the same key that was used for encryption.

Now will move on Conventional encryption

In conventional encryption, it is assumed that it is mathematically impossible to derive the plaintext from the ciphertext without the key.[R1] Therefore, it is essential that the key remains secret.

These encryption algorithms are used in practice due to their efficiency in encrypting/decrypting but these algorithms have vulnerabilities. One aspect of these vulnerabilities is the total number of keys available to choose from. Larger key domains reduce possibility of brute force attacks. The key length is another aspect of these vulnerabilities since they will produce periodic patterns in the ciphertext. Longer keys often reduce periodicity. The goal of conventional encryption algorithms is to produce truly randomized ciphertexts, such that the use of frequency analysis on individual ciphertext symbols or ciphertext blocks is useless.