What is speck?

Speck is a family of lightweight block ciphers developed by the National Security Agency (NSA) in 2015. It's designed to be efficient in hardware and software implementations, particularly in resource-constrained environments such as embedded systems and IoT devices.

Here's a summary of key aspects:

• Design Philosophy: Speck prioritizes performance and simplicity. It achieves this through an Add-Rotate-XOR (ARX) design, which relies on bitwise addition, bitwise rotation, and bitwise XOR operations. These operations are highly efficient on a wide range of platforms.

• Block and Key Sizes: Speck supports various block and key sizes, allowing for flexibility in security level and performance trade-offs. Common combinations include Speck64/128 (64-bit block, 128-bit key), Speck128/256 (128-bit block, 256-bit key), and others. The designation generally refers to Speck + BlockSize / KeySize.

• ARX Structure: The core round function of Speck consists of a simple ARX network. Two branches are updated in each round using addition, rotation, and XOR operations. This structure is easy to analyze and implement.

• Key Schedule: Speck's key schedule is designed to be simple and efficient, generating round keys from the main key.

• Security Considerations: While Speck has been extensively analyzed, some concerns have been raised regarding its security margins, especially with reduced round versions. Differential and linear cryptanalysis are primary areas of focus for its evaluation. Speck is generally considered secure when used with recommended parameters (block sizes, key sizes, and number of rounds).

• Use Cases: Speck is suitable for applications where performance and low power consumption are critical, such as in embedded systems, IoT devices, and resource-constrained environments. It can be used for data encryption, authentication, and other security functions.

Key subjects:

• Block Cipher
• Lightweight Cryptography
• ARX Design
• Key Schedule
• Cryptanalysis