Private and Public Key Cryptography
In symmetric cryptography or private key cryptography, there is generally an encryption key. The encryption process, whereby the key is applied onto a clear text message via an algorithm, turns it into an encrypted message, which will now look rather random and hard to read. Using the same secret key, you can also decrypt the message, by using the same key and applying it onto the encrypted message via an algorithm, turning it back into clear text. This implies that the secret key must be shared and kept private by both the sender and the receiver. To use a symmetric cryptography encryption scheme, the sender and receiver must securely share the secret key in advance.
Public key cryptography, also known as asymmetric cryptography uses two separate keys, a public key and a private key. The Public Key is made available to everyone via a publicly accessible repository or directory. On the other hand, the Private Key must remain confidential to its respective owner. Because the key pair is mathematically related, whatever that is encrypted with a Public Key may only be decrypted by its corresponding Private Key and vice versa. The owner encrypts a message with one of the keys, and uses the other key to decrypt it. The general idea is that you generate two keys, publish one as public key, and keep the other one, the private key, well protected and private.
Suppose that Karen encrypts a message with John's public key. The message cannot be decrypted by anyone who does not possess the matching private key. Only John has access to his corresponding Private Key and as a result is the only person with the capability of decrypting the encrypted data back into its original form. So using someone else's public key gives you a way to send them a message no-one else can read. This will ensure confidentiality in messages exchanged.
Now, suppose Karen encrypts a message with her private key. Using Karen's public key, John can decrypt the message. This verification proves that Karen had access to the private key, and therefore is likely to be the person associated with the public key. This would be a form of a digital signature. This also ensures that the message has not been tampered, as any manipulation of the message will result in changes to the encoded message digest, which otherwise remains unchanged between the sender and receiver.
In practice, however, not every encryption in transaction will use public key cryptography method as it is much slower than symmetric cryptography. Normally, at the initial stage, John will send a message encrypted with Karen's public key that says "I want to talk to you securely.". Karen sends a reply encrypted with John's public key that says "Ok, we'll use this private key for all future messages." John and Karen can then communicate securely using the faster symmetric cryptography encryption algorithm. So they have all of the benefits of public key cryptography without the cost of doing public key encryption on every message.
There are other scenarios where public key cryptography can be used. For example, if Karen encrypts a message with John's public key, then further encrypts the result with her private key, then the resulting message must have come from her, and it can only be read by John. This gives the two a secure authenticated way to communicate.
Cryptography is an area of research that arguably generates a high level of interest. However, we need to realize that no encryption scheme is unbreakable. The transmission of secure data typically relies on encryption and decryption "keys" generated by sophisticated algorithms and swapped between sender and receiver so encrypted data can be decrypted. These keys are generally considered secure, but their degree of security is highly dependent on how much computing power a third party has at its disposal. Encryption strength and the number of bits used in the keys are selected based on how many decades the data needs to be kept safe. In other words, even the best standard encryption that is considered unbreakable today will be vulnerable at some point in the future.
Public key cryptography, also known as asymmetric cryptography uses two separate keys, a public key and a private key. The Public Key is made available to everyone via a publicly accessible repository or directory. On the other hand, the Private Key must remain confidential to its respective owner. Because the key pair is mathematically related, whatever that is encrypted with a Public Key may only be decrypted by its corresponding Private Key and vice versa. The owner encrypts a message with one of the keys, and uses the other key to decrypt it. The general idea is that you generate two keys, publish one as public key, and keep the other one, the private key, well protected and private.
Suppose that Karen encrypts a message with John's public key. The message cannot be decrypted by anyone who does not possess the matching private key. Only John has access to his corresponding Private Key and as a result is the only person with the capability of decrypting the encrypted data back into its original form. So using someone else's public key gives you a way to send them a message no-one else can read. This will ensure confidentiality in messages exchanged.
Now, suppose Karen encrypts a message with her private key. Using Karen's public key, John can decrypt the message. This verification proves that Karen had access to the private key, and therefore is likely to be the person associated with the public key. This would be a form of a digital signature. This also ensures that the message has not been tampered, as any manipulation of the message will result in changes to the encoded message digest, which otherwise remains unchanged between the sender and receiver.
In practice, however, not every encryption in transaction will use public key cryptography method as it is much slower than symmetric cryptography. Normally, at the initial stage, John will send a message encrypted with Karen's public key that says "I want to talk to you securely.". Karen sends a reply encrypted with John's public key that says "Ok, we'll use this private key for all future messages." John and Karen can then communicate securely using the faster symmetric cryptography encryption algorithm. So they have all of the benefits of public key cryptography without the cost of doing public key encryption on every message.
There are other scenarios where public key cryptography can be used. For example, if Karen encrypts a message with John's public key, then further encrypts the result with her private key, then the resulting message must have come from her, and it can only be read by John. This gives the two a secure authenticated way to communicate.
Cryptography is an area of research that arguably generates a high level of interest. However, we need to realize that no encryption scheme is unbreakable. The transmission of secure data typically relies on encryption and decryption "keys" generated by sophisticated algorithms and swapped between sender and receiver so encrypted data can be decrypted. These keys are generally considered secure, but their degree of security is highly dependent on how much computing power a third party has at its disposal. Encryption strength and the number of bits used in the keys are selected based on how many decades the data needs to be kept safe. In other words, even the best standard encryption that is considered unbreakable today will be vulnerable at some point in the future.
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