Quantum cryptography uses quantum mechanics to generate a private and secure key for encryption. It involves the transmission of polarized photons that are received and decoded using corresponding filters. The exchange of information to generate a shared key can detect eavesdropping and generate a new key if necessary. Once a key is generated, an encryption algorithm can be used to send a secure message. However, the specialized equipment required may hinder its widespread use.
Quantum cryptography is a form of encryption that relies on the principles of quantum mechanics to protect data and detect eavesdropping. Like all forms of encryption, quantum cryptography is potentially unbreakable, but is theoretically extremely reliable, which could make it suitable for very sensitive data. Unfortunately, it also requires some very specialized equipment, which could hinder the spread of quantum cryptography.
Cryptography involves exchanging coded messages. The sender and recipient have the ability to decrypt messages, thereby determining their content. The key and the message are usually sent separately, as one is useless without the other. In the case of quantum cryptography, or quantum key distribution (QKD) as it is sometimes known, quantum mechanics is involved in generating the key to make it private and secure.
Quantum mechanics is an extremely complex field, but the important thing to know about cryptography is that observing something causes a fundamental change in it, which is key to how quantum cryptography works. The system involves the transmission of photons that are sent through polarized filters and the reception of polarized photons on the other side, with the use of a corresponding set of filters to decode the message. Photons are an excellent tool for cryptography, as they can be assigned a value of 1 or 0 depending on their alignment, creating binary data.
Sender A would initiate the data exchange by sending a series of randomly polarized photons which could be polarized rectilinearly, causing a vertical or horizontal orientation, or diagonally, in which case the photon would tilt in one direction or the other. These photons would arrive at recipient B, who would use a randomly assigned set of straight or diagonal filters to receive the message. If B used the same filter that A used for a particular photon, the alignment would match, but if he didn’t, the alignment would be different. Next, the two exchanged information about the filters they used, discarding photons that didn’t match and keeping those that did to generate a key.
When the two exchange information to generate a shared key, they can reveal the filters they use, but they don’t reveal the alignment of the protons involved. This means that this public information cannot be used to decrypt the message, as an eavesdropper would be missing a critical part of the key. More critically, the exchange of information would also reveal the presence of an eavesdropper, C. If C is to eavesdrop to obtain the key, it will have to intercept and observe the protons, altering them and alerting A and B to the presence of an eavesdropper. The two can simply repeat the process to generate a new key.
Once a key is generated, an encryption algorithm can be used to generate a message that can be sent securely over a public channel, as it is encrypted.
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