A private key, also known as a secret key, is a cryptographic variable used with an algorithm to encrypt and decrypt data. Only the key's generator or those authorized to decrypt the data should know the secret key. Private keys are crucial in symmetric and asymmetric cryptography, as well as cryptocurrencies.
Typically, a private key is a lengthy, randomly or pseudo-randomly generated sequence of bits that is difficult to deduce. The complexity and length of the private key determine the strength of the encryption algorithm and influence how easily a brute-force attack may be launched.
How Are Private Keys Used?
Private key encryption is also referred to as symmetric encryption, where the same private key is used for both encryption and decryption. Private keys are also utilized in asymmetric cryptography, also known as public key cryptography. In this case, the private key refers to the secret key of a public key pair. In public key cryptography, the private key is used for encryption and digital signatures.
Besides encrypting and decrypting data, there are many applications of private keys, including web server security, digital signatures and document signing, digital identities, and cryptocurrencies.
Machine-to-machine communications and man-in-the-middle attacks
Together with their corresponding public keys, private keys serve as the basis for the SSL/TLS security protocols that form the foundation of HTTPS. Without SSL certificates or TLS to establish secure connections between servers and other public-facing machines and devices, cybercriminals might exploit open connections using a range of attack vectors, such as man-in-the-middle assaults, to intercept and compromise the confidentiality and integrity of important information flows. The combination of private and public keys helps defeat man-in-the-middle attacks by validating the identities of the recipient and sender.
Digital signatures and document signing
In addition to encrypting data, private and public key pairs can also be used to create digital signatures and sign documents. A document is digitally signed using the sender's private key, while the public key is used to validate the sender's digital identity. This cryptographic validation mathematically links the signature to the original message to ensure that it has not been altered.
Public key and private key pairs are also effective for authenticating machine identities. As data and applications sprawl beyond traditional networks to mobile devices, public and private clouds, and Internet of Things (IoT) devices, machine identity protection becomes more crucial than ever before. Digital identities are not limited to devices; they may be used to verify people, data, and applications as well. Digital identity certificates with asymmetric cryptography enable enterprises to enhance their security by removing passwords, which attackers have become increasingly effective at compromising.
To generate, store, and trade digital currency, cryptocurrencies rely on cryptographic algorithms. Cryptocurrencies employ public key cryptography to generate digital signatures that authenticate value transfers and symmetric encryption to secure data exchanges.
How Do Private Keys Work?
When private keys are used in the context of symmetric encryption, they work as follows:
- Generate a new private key. Prior to encrypting a message, a new key is generated that is as random as feasible using specialized encryption software.
- Securely store the private key. After generation, the private key must be safely kept. Keys may be stored offline or on the machine used to generate, encrypt, and decrypt data, depending on the application. For enhanced security, private keys may be either password-protected, encrypted, or hashed — or all three.
- Key exchange. Since the private key is also needed to decipher as well as encrypt, employing it for symmetric encryption requires a key exchange to securely share it with parties authorized to exchange encrypted data. Typically, cryptographic software is used to automate this procedure.
- Key management. Private key management is necessary to prevent the misuse of any individual key. It facilitates the retirement of keys when their useful lifetime has expired.
If the private key is part of public key encryption, the same steps with some functional differences are followed:
- Generate the public-private key pair, using cryptographic software to ensure randomness.
- Securely store the private, just like in symmetric encryption.
- The private key of a public key pair should never be shared with others. Public key cryptography is used to securely exchange session keys utilized for symmetric encryption.
- Public key pairs are frequently established with expiration dates, and key management is essential for preserving access to data secured with a key pair.
Private keys vs. public keys
In symmetric encryption, the same secret key is used to encrypt and decode data, whereas in asymmetric cryptography, also known as public key cryptography, public and private keys are utilized. These two distinct but mathematically related keys are used to convert plaintext to ciphertext or ciphertext back to plaintext.
When the public key is used to encrypt ciphertext, only the private key may be used to decrypt the ciphertext. With this method, anyone with access to the public key can encrypt a message, but only the owner of the private key can decrypt it.
When the private key is used to encrypt ciphertext, the public key can be used to decrypt the ciphertext. This ciphertext may be incorporated into a digital signature and used to verify the signature. Only the owner of the private key could have encrypted ciphertext, therefore the digital signature is validated if the associated public key successfully decrypts it.
The public key is made accessible to anyone who needs it. It is obtained via a repository that is open to the public. The private key is confidential and should only be accessible to the owner of the public key pair. In this manner, decryption of data encrypted with the public key requires the corresponding private key, and vice versa. Typically, public key encryption is used to secure communication channels like email.
Advantages of private encryption keys
Encryption using a private key offers various advantageous characteristics. They include four benefits, these include:
- More secure. Longer private keys with increased entropy, or randomness, are more resistant to brute-force and dictionary attacks.
- Faster. On a computational level, symmetric key encryption is faster than asymmetric encryption with its public-private key pairings.
- Optimal for encryption. The majority of cryptographic methods encrypt data transmissions with private key encryption. Typically, they use a public key algorithm to share secret keys securely.
- Work with block and stream ciphers. Secret key ciphers — the mechanism for encrypting and decrypting data — fall into either stream ciphers or block ciphers. A block cipher simultaneously applies a private key and algorithm to a block of data, whereas a stream cipher applies the key and algorithm bit by bit.
Challenges of private encryption key management
The security of encryption keys is contingent upon the selection of a robust encryption method and the maintenance of high operational security standards. Encryption key management is required for every organization that encrypts data. This applies to both symmetric and asymmetric encryption.
While private key encryption can provide a high level of security, the following key management issues must be considered:
- Overall management. Management of encryption keys is required to safeguard cryptographic keys against loss, compromise, and unwanted access.
- Continuous upgrading. Private keys used to encrypt sensitive data should be changed frequently to reduce their vulnerability if they are leaked or stolen.
- Recovery potential and loss. If a key to encrypt data becomes inaccessible, the data encrypted with that key will be irretrievable and lost.
Secure Your Machine Identity
Maintaining security for all sorts of communication requires protecting the private keys needed to protect that data. If you are interested in learning more about private keys and how they should be managed, download our SSH Machine Identity Management for Dummies guide.