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#ALICE MADNESS RETURNS PRODUCT KEY GENERATOR SERIES#

The compromise of the private key would still open up the possibility of future man-in-the-middle attacks so.Īn asymmetric-key is necessary for signing messages, but asymmetric ciphers are slow to use in comparison to symmetric ciphers. This means the compromise of of a session key cannot compromise past messages, nor could the compromise of the long lived private key. Let’s finally tie this all together by looking at the concept of forward secrecy.Īlso known as perfect forward secrecy (PFS), this implementation of cryptography provides security of past sessions against future secret keys being compromised.Ī asymmetric system counts as having forward secrecy if it generates one random shared key per session, and uses the long lived asymmetric private key only for signing messages.

#ALICE MADNESS RETURNS PRODUCT KEY GENERATOR SERIES#

Two prime numbers are chosen at random, and then have a series of steps performed on them to create the values of e, d, and N.Ī list of mathematical steps here looses all context, so instead I would recommend watching this maths teacher explain it far better than I ever could: So how were the two keys above generated? Obviously they are extremely simplified examples, and use much smaller numbers than would ever be used in reality, but are still valid.Įach key can be represented as (e, N), (d, N). Remember, the reverse of this can be done (signing a message with a private key and decrypting using a public key) as described in ‘Authentication using key pairs’ earlier. As you’ve read this far you’re likely not surprised this gives us… 2!.

Alice can use this to do the sum: 4**11(mod14).

Alice has access to her private key, Key 2 - (11, 14).

So now Alice gets a message of ‘4’ and must decrypt it.

This equals 4 (which if we wanted to represent as a letter we would use 4 = D as agreed on in point one).

We use Alice’s public Key 1 to encrypt this integer, using the sum: 2**5(mod14).

This would be agreed by both parties and does not need to be secure. For simplicity we will say B = 2, as it is the second letter of the Latin alphabet.

We convert B to an integer, as our algorithm is based in numbers, not letters.

Let’s say we are Bob and the message we want to send to Alice is simply the letter ‘B’. Asymmetric-key pairs are often used to establish initial communication, authentication when needed, while a symmetric key can be used for message encryption from that point forwards.

Alice can then decrypt the ciphertext message using her private key and read it, confident it is from Bob.Īsymmetric algorithms are relatively slow compared to symmetric algorithms, we will look at this further when looking at forward secrecy.

If the result of this matches the ciphertext message then Alice knows that Bob sent the message, as only Bob’s private key could have encrypted the message in a way Bob’s public key could decrypt it to match.

Alice uses Bob’s public key to decrypt the signature.

Bob sends both the ciphertext message and the signature to Alice.

Only Bob’s public key will be able to decrypt this.

He encrypts his ciphertext message with his own private key. Only Alice’s private key can decrypt this. Bob encrypts the plaintext message with Alice’s public key.Alice is able to authenticate it was Bob who sent the messageĪn incredibly important benefit of key pairs is the ability to authenticate the sender of a message.