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Blog Security A Beginner’s Guide to Understanding Private Keys


JUNE 7 2023


Table of Contents

Private Key: What It Is, How It Works, Best Ways to Store

A private key, also known as a secret key, is a crucial component of asymmetric encryption that ensures secure communication. It is a secret value that is kept confidential and only known to its owner, allowing them to decrypt messages sent to them. In this brief, we will explore the importance of private keys, how they work, and the potential risks associated with their misuse or compromise. Understanding private keys is essential for anyone involved in secure communication, from individuals to businesses and organizations.

What Is a Private Key?

A private key is a key known only to its owner. Only keeping the private key secret guarantees the impossibility of forging a document and a digital signature by an attacker. Like other cryptographic keys, a private key can be used by a cryptographic algorithm when encrypting/decrypting messages, setting and verifying a digital signature, and calculating authentication codes (MACs).

When using the same algorithm, the encryption result depends on the key. For modern algorithms of strong cryptography, the loss of a key makes it practically impossible to decrypt the information. The amount of information in a key is usually measured in bits.

According to Kerchhoff’s principle, the strength of a cryptographic system should be determined by the concealment of secret keys, but not by the concealment of the algorithms used or their features.

How Does a Private Key Work?

In symmetric cryptosystems, the same secret key is used for encryption and decryption. Hence the name – symmetrical. The algorithm and the key are chosen in advance and are known to both parties. Keeping the key secret is an important task for establishing and maintaining a secure communication channel. In this regard, there is a problem with the initial key transfer (key synchronization). In addition, there are methods of crypto attacks that allow one way or another to decrypt information without a key or by intercepting it at the negotiation stage. In general, these points are the problem of the cryptographic strength of a particular encryption algorithm and are an argument when choosing a particular algorithm.

Symmetric, and more specifically, alphabetic encryption algorithms were among the first algorithms. Later, asymmetric encryption was invented, in which the interlocutors have different keys.

Scheme for implementing the encryption algorithm with a secret key:

There are two interlocutors – Alice and Bob, who want to exchange confidential information.

  1. Key generation. Bob (or Alice) chooses an encryption key d and algorithms E, and D (encryption and decryption functions), then sends this information to Alice (Bob).
  2. Encryption and transmission of the message. Alice encrypts message m using the received key d: E(m,d)=c. And sends the received ciphertext c to Bob. Bob does the same if he wants to send a message to Alice.
  3. Message decryption. Bob (Alice), using the same key d, decrypts the ciphertext c: D(c,d)=m

Private Keys and Digital Wallets

The private key is a secret alphanumeric password/number used to pay or send your cryptocurrencies to another Bitcoin public address. This is a 256-bit number that is randomly selected as soon as you create a digital wallet.

The degree of randomness and uniqueness is well generated by cryptographic functions for security purposes.

Here is what a Bitcoin private key looks like (it always starts with 5):


Private keys are used to make irreversible transactions. They are the key to spending and sending your funds to anyone, anywhere. This irreversibility is guaranteed by the mathematical signatures that are associated with every cryptocurrency transaction whenever we use private keys.

And for each transaction, these signatures are unique, even if they are generated from the same private keys. This feature makes them impossible to copy. The user can confidently use the same private key over and over again.

In addition, signatures are mathematically related to Bitcoin addresses. This mathematical relationship helps to confirm that the signatures belong only to the specific account holder who wants to transfer bitcoins.

Digital keys are critical to owning cryptocurrencies. These private keys are not stored on most blockchains, they are created and stored in a file or wallet. There are many types of wallets, and some allow users to store and protect private keys. Cold wallets store private keys offline to minimize the risk of hacking. In hardware wallets private keysare stored there on a password-protected physical device.

Therefore, when choosing a wallet, you must first of all study how and where private keys are stored, and whether they can be downloaded to your computer.

Advantages of Private Encryption Keys

In symmetric systems, private encryption keys are chosen at random, and their generally accepted length usually varies between 128 and 256 bits, depending on the required level of security. In asymmetric encryption, there must be a mathematical relationship between the public and private keys, that is, they are connected by a certain mathematical formula.

For this reason, attackers can use this pattern to break the cipher, in turn, asymmetric keys must be much longer to provide an equivalent level of security. The difference in key length is so significant that an AES 128-bit symmetric key and a 2048-bit asymmetric RSA key pair could provide about the same level of security.

Challenges of Private Encryption Key Management

Symmetric encryption, used by itself as a means of protecting sensitive data being sent, can be very costly simply because of the difficulty of transmitting a secret key. To establish an encrypted communication using a symmetric algorithm, the sender and recipient must first agree on a key and keep it secret. If they are located in geographically remote locations, then they must resort to the help of a trusted intermediary to avoid compromising the key during transport.

An attacker who intercepts the key in transit will be able to later read, modify and forge any information encrypted or certified by this key. The global problem with symmetric ciphers is the complexity of private key management: how do you deliver the key to the recipient without the risk that it will be intercepted?

Private Keys vs. Public Keys

Compared to public key cryptography, single secret key algorithms have the following advantages:

  • encryption and decryption speed
  • ease of implementation due to simpler operations
  • a shorter key length is required for comparable durability


An important disadvantage of symmetric ciphers is the impossibility of their use in the mechanisms for generating electronic digital signatures and certificates since the key is known to each party. In addition, a serious problem in such systems is the complexity of the key exchange. For application, it is necessary to solve the problem of reliable transmission of keys to each subscriber, since a secret channel is needed to transmit each key to both parties.

To compensate for the shortcomings of private key encryption, a combined (hybrid) cryptographic scheme is currently widely used, where a session key is transmitted using asymmetric encryption, which is used by parties to exchange data using symmetric encryption. The most common example is the TLS protocol used to establish secure HTTPS connections when the web site SSL certificate is verified by a trusted Certificate Authority CA and all communications are encrypted with a session key.

Generating Secure Private Keys

Generating secure private keys is a critical step in ensuring the confidentiality and integrity of sensitive information in cryptography. It involves creating a unique and unpredictable key that can only be accessed by its owner. Users can create private keys that are highly resistant to attacks and ensure the security of their encrypted communication.


For modern symmetric algorithms (AES, CAST5, IDEA, Blowfish, Twofish), the main characteristic of cryptographic strength is the key length. Encryption with keys of 128 bits or more is considered strong since it takes years of powerful supercomputers to decrypt information without a key. For asymmetric algorithms based on problems of number theory (the factorization problem – RSA, the discrete logarithm problem – Elgamal), due to their features, the minimum reliable key length is currently 1024 bits.

For asymmetric algorithms based on the use of the theory of elliptic curves ECDSA, the minimum reliable key length is 163 bits, but lengths of 191 bits and more are recommended.


The key generation system ensures the compilation of cryptographically strong keys through the use of a random number generator or a pseudo-random number generator. The generation algorithm itself must be secure since much of the security provided by encryption lies in the security of the key.

If the choice of keys is left to users, then they are more likely to choose keys like “Barney” than “*9(hH/A”, simply because “Barney” is easier to remember. And these kinds of keys are very quickly picked up by a dictionary attack, and here even the most secure algorithm will not help. In addition, the generation algorithm ensures the creation of statistically independent keys of the desired length, using the most cryptographically strong alphabet.

For example, to generate the SSH keys one can use the standard OpenSSH tools that contains the ssh-keygen utility, which is used to generate SSH key pairs. You can run it on a local computer and generate for example a 2048-bit RSA key pair. You should select a location for the key and you’ll be prompted to enter a passphrase which encrypts the private key file on disk to secure its storage. Now you have an SSH key pair that you can use to authenticate. You can share the SSH public key wherever it is needed.

Use of Private Keys in Cryptocurrencies

Ownership of a private key means ownership of the crypto assets (coins and tokens) associated with that key. Anyone who knows this private key can send cryptocurrency to any address. Therefore, the compromise (theft or disclosure) of the private key means the loss of the cryptocurrency at the corresponding address.

Private keys in cryptocurrency wallets can be generated in two ways: using a random number generator and based on a secret phrase (seed phrase). The first method is more reliable since there is no additional vulnerability in the form of compromise of the secret phrase. The second one is faster and more convenient since you can generate any number of addresses from one master key, and it is easier for people to work with a set of ordinary words than with a separate long string of random characters for each address.

To take possession of cryptocurrencies, it is not necessary to steal a single copy of the private key, it is enough to copy a string of characters – for example, take a picture of the printed key or copy a text file with it.

What Is the Best Way to Store Private Keys?

You can increase security if you store the secret key on a token or smart card. In such devices, the key is generated on the hardware itself and is not exported. The private key never leaves the device, making it very difficult for an outsider to gain unauthorized access and compromise. Also, when using a token, each time you use a certificate, you must enter a password. This means that even if someone gets your token, they will still need a password. Also with a token, you can securely use the same certificate on multiple computers without having to make multiple copies.

HSM is another hardware private key storage solution, especially if you don’t want to rely on individual tokens or it seems too burdensome. While tokens are more focused on manual entry or individual applications, HSMs provide APIs and support automated workflows, and automated builds. They are also FIPS compliant and generally provide a higher degree of compliance than tokens.


Private keys are a fundamental component of modern cryptography, ensuring the confidentiality and integrity of sensitive information. It is essential to generate and store private keys securely to prevent unauthorized access or compromise. By following best practices and regularly updating keys, users can maintain the security of their communications. Helenix has unique expertise in cryptographic solutions development, cryptographic key lifecycle protection and management, which you can learn about in detail in the Custom Development section.


A private key is a long string of characters used in asymmetric encryption. An example of a private key is a 256-bit hexadecimal value that is randomly generated and unique to the user.

Private keys are typically generated using a random number generator and kept secret. They can be obtained by creating a new keypair using a cryptographic tool or extracted from an existing wallet.

Yes, a private key is also known as a secret key. It is a cryptographic key that is kept confidential and known only to its owner, while the corresponding public key is freely shared for encryption and verification.

Custodial wallets are convenient for their ease of use, but they require users to trust a third party to secure their private keys. This increases the risk of theft or loss of funds. It is recommended to use non-custodial wallets to retain full control over private keys.