Public Key Cryptography (PKC), also known as asymmetric cryptography, is an encryption system that uses a pair of keys: a public key and a private key. The pairs give PKC a unique set of characteristics and capabilities that can be utilized to solve challenges inherent in other cryptographic techniques.
How Does Public Key Cryptography Work?
In PKC scheme, the public key is used by a sender to encrypt information, while the private key is used by a recipient to decrypt it. It is computationally infeasible to compute the private key based on the public key. Hence, public key can be shared freely, allowing users an easy and convenient method for encrypting content and verifying digital signatures, and private keys can be kept secret, ensuring only the owners of the private keys can decrypt content and create digital signatures.
Because asymmetric encryption algorithms generate key pairs that are mathematically linked, their key lengths are much longer than those used in symmetric cryptography. This longer length – typically between 1,024 and 2,048 bits – makes it extremely difficult to compute a private key from its public counterpart. One of the most commons algorithm for asymmetric encryption in use today is known as RSA.
In the RSA scheme, keys are generated using a modulus that is arrived at by multiplying two numbers (often two large prime numbers). In simplest terms, the modulus generates two keys; one public that can be shared, and one private that should be kept in secret.
The applications for public key cryptography are as follow:
- Digital Signatures – Content is digitally signed with an individual’s private key and is verified by the individual’s public key;
- Encryption – Content is encrypted using an individual’s public key and can only be decrypted with the individual’s private key.
PKC also features prominently in blockchain and cryptocurrency technology. When a new cryptocurrency wallet is set up, a pair of keys is generated (public and private keys). The wallet address is generated using the public key and can be securely shared with others. The private key, on the other hand, is used for creating digital signatures and verifying transactions, and therefore, must be kept in secret. Once a transaction has been verified by confirming the hash contained in the digital signature, that transaction can be added to the blockchain ledger. This system of digital signature verification ensures that only the person who has the private key associated with the corresponding cryptocurrency wallet can release funds from it.
It should be noted that the asymmetric ciphers used in cryptocurrency applications are different from those used for computer security purposes. Bitcoin and Ethereum, for instance, use a specialized cipher known as the Elliptic Curve Digital Signature Algorithm (ECDSA) to verify transactions.
Despite it can be used to enhance computer security and provide verification of message integrity, PKC does have limitations. Owing to the complex mathematical operations involved in encryption and decryption, asymmetric algorithms can be quite slow when forced to deal with large amounts of data. This type of cryptography also depends heavily on the assumption that the private key will remain secret. If a private key is accidentally shared or exposed, the security of all messages that have been encrypted with its corresponding public key will be compromised. It is also possible for users to accidentally lose their private keys, in which case it becomes impossible for them to access the encrypted data.
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