Encryption
Encryption is the process of converting data into an unreadable format to ensure confidentiality. Its crucial center is that it relies on cryptographic algorithms and one or more keys to protect information from unauthorized access.
Unlike encoding, encryption is designed to be reversible only for those who have the correct key, making it essential for secure communication, data protection, and privacy.
A main concept in cryptography is the Key Size, which refers to the number of bits used in a cryptographic key. This gives a measure of how many possible different keys there are, and the resistance against brute-force attacks. For example, a 128-bit key has 2128 possible combinations, a 256-bit key has 2256 possible combinations, and so on.
It is also important to implement encryption correctly and to use strong keys to avoid possible attacks and maintain the data secure. There are two main types of encryption, which are used in different scenarios, with necessities like security, speed, efficiency, and ease of use that need to be covered.
Symmetric
Also called secret-key encryption, uses the same key for both encryption and decryption. It’s fast, efficient, and ideal for encrypting large volumes of data.
It's important to know that if the key is compromised, all of the data that was encrypted with that key will be able to be decrypted.
Its main characteristics are:
Both parties need to share the secret key before the communication and keep it secure
Used when the priority is speed and efficiency are priority
Faster than symmetric encryption but with less key size
Usually used to protect files, communications, databases, embedded systems, and secure tunnels in network protocols such as VPNs, TLS, or SSH
Some examples are AES, DES, 3DES, RC4, Blowfish
Asymmetric
Asymmetric encryption uses a pair of keys, the first one known as the public key, to encrypt the information, and the second one as the private key, to decrypt it. The public key can be shared with anyone, but the private key must be kept secret.
The sender uses the public key of the recipient to encrypt the data, and in this way, the data can only be decrypted with the private key of the same recipient.
It's widely used in secure messaging, digital signatures, and key exchange.
Slower than symmetric encryption, but considered more secure, as the secret is only known by the owner and not shared with anyone
Typically used for encrypting small amounts of data, secure key exchange, and digital signatures
Some examples are RSA, DSA, ECDH, ECC
Signatures
Signatures are used to provide authentication, integrity, and non-repudiation of data. Unlike encryption, which hides content, a signature confirms that a message or file was genuinely created by a known sender and has not been altered in transit.
It works oppositely to the encryption process, where a user uses the private key to sign a message, and anyone can use the corresponding public key to verify it. This creates a verifiable link between the message and the signer without revealing the private key.
A stablished practice in signatures is first hashing the original data before signing it, instead of signing the full message directly. This makes signing efficient and ensures that even the slightest change in the original message leads to a completely different signature, ensuring data integrity and source authenticity.
Digital signatures are widely used in:
Secure software updates and package signing
TLS certificates for HTTPS
Email authenticity (PGP, S/MIME)
Blockchain transactions
It is vital to use secure key lengths, resistant hash functions, and proper padding schemes to avoid signature forgery and hash collision attacks, as well as secure implementation and key management.
Public and Private Key Role Importance
The public and private keys have specific roles to allow operations to be reversed and verified correctly. These have to be respected to maintain the purposes of operations without compromising confidentiality or authenticity.
For example, let's think of a reversed scenario for encryption:
The public is only known by the owner, and the private key is known by everyone
This means that anyone could decrypt messages meant for us, as everyone has our private key, and nobody could encrypt a message for us, as anyone has our public key
The result is that there is no confidentiality, as no one can send us encrypted messages, and any encrypted data is public
Now, let's think of a reversed scenario for encryption:
Only the owner has the public key, and everyone has the private key
This means that anyone could generate a signature pretending to be us, and only we could verify it, but no one else could trust it
The result is that the signatures are meaningless, as anyone can forge them, and no one else can verify them
In conclusion, the public and private keys cannot be arbitrarily swapped unless the context explicitly allows it:
Encrypting a message with a private key is not encryption in the confidentiality sense; it’s signing
Decrypting with a public key is not decryption in the confidentiality sense; it’s signature verification
For secrecy, we must use the flow public → private, and for authenticity, the flow private → public
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