Public-key cryptology?

Question

Today in my computer class, we learned about ssl and public-key cryptology. I had a question that my teacher couldn't answer though so I'm posting it here. According to the teacher it is impossible to guess the private key based on the public key and it is also impossible to decrypt a message with the public key that was encrypted with the public key. My question is, why is the public key able to encrypt the message but it can't be used to work backwards to decrypt it?

Answer 1

extract from Wikipedia source article:



.....a public key algorithm does not require a secure initial exchange of one, or more, secret keys between the sender and receiver. These algorithms work in such a way that, while it is easy for the intended recipient to generate the public and private keys and to decrypt the message using the private key, and while it is easy for the sender to encrypt the message using the public key, it is extremely difficult for anyone to figure out the private key based on their knowledge of the public key. They are based on mathematical relationships (most notably the integer factorization and discrete logarithm problems) which have no efficient solution.

Answer 2

Public-key cryptography refers to a cryptographic system requiring two separate keys, one to lock or encrypt the plaintext, and one to unlock or decrypt the cyphertext. Neither key will do both functions. One of these keys is published or public and the other is kept private. If the lock/encryption key is the one published then the system enables private communication from the public to the unlocking key's owner. If the unlock/decryption key is the one published then the system serves as a signature verifier of documents locked by the owner of the private key.

Answer 3

Public key cryptography (ie. the cryptography that makes use of a private-key and public key) is needed because of the fact it enables 2 events who've in no way exchanged preparation earlier, to envision a secure channel of verbal replace. classic cryptography (ie. symmetric) continually required that a pre-arranged key or secret be established by some depended on courier. Public key crypto is what makes it possible to have maintain transactions on line.