The exchange of a shared secret between a server and a client can be achieved with public-key cryptography:. After getting the symmetric key from the server, we can use CryptoKit to create a SymmetricKey type for further usage:. The current state of the art in symmetric-key encryption is a cipher called AEAD.
We already looked at signing with public-key cryptography in the previous article. For that, we use the previously shared secret key to sign the digest of the data and then send both, the data and the signed digest to the server. The server uses the same key to validate the data. In the code example above, authenticationCode is our signed digest that we send to the server along with the actual data.
Checking the validity of authenticationCode is similarly simple:. And that's basically it. CryptoKit allows us to apply symmetric cryptography signing, encrypting and decrypting data with a few lines of code. That's pretty awesome! Receive a monthly newsletter about the latest articles and tips. Cryptographic hash functions in CryptoKit for iOS. Use cases of cryptographic hash functions and how to implement them in iOS. Public-key cryptography with CryptoKit for iOS.
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Block ciphers are typically considered to be more powerful and practical primitives than stream ciphers, but they're also slower. Stream ciphers encrypt each unit of plaintext such as a byte , one unit at a time, with a corresponding unit from a random key stream. The result is a single unit of ciphertext. These algorithms are useful for authentication and for establishing secure communication channels when it is inconvenient to share a symmetric key in advance.
An encryption scheme is called asymmetric if it uses one key — the public key — to encrypt and a different, but mathematically related, key — the private key — to decrypt. It must be computationally infeasible to determine the private key if the only thing one knows is the public key.
Therefore, the public key can be distributed publicly while the private key is kept secret and secure. Together the keys are referred to as a key pair. Another more common name for asymmetric encryption is public-key cryptography. Public-key cryptography is typically based on mathematical problems that are relatively easy to perform but cannot be easily reversed.
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Symmetric-key cryptography is a term used for cryptographic algorithms that use the same key for encryption and for decryption. In practice, both symmetric-key cryptography and asymmetric-key cryptography are often combined to secure data. Asymmetric-key cryptography is. Symmetric encryption requires a strong and secure infrastructure to keep keys and data secure. This is what a hardware security module (HSM).