Add a table summarizing the differences between the variants

README.md

@@ -16,6 +16,20 @@ Portable C implementations of the [AEGIS](https://datatracker.ietf.org/doc/draft
 - Unauthenticated encryption and decryption (not recommended - only implemented for specific protocols)
 - Deterministic pseudorandom stream generation.
 
+## Key differences between AEGIS variants
+
+| **Feature**          | **AEGIS-128L**                                                        | **AEGIS-256**                                | **AEGIS-128X2**                                 | **AEGIS-128X4**                                 | **AEGIS-256X2**                                 | **AEGIS-256X4**                                 |
+| -------------------- | --------------------------------------------------------------------- | -------------------------------------------- | ----------------------------------------------- | ----------------------------------------------- | ----------------------------------------------- | ----------------------------------------------- |
+| **Key Length**       | 128 bits                                                              | 256 bits                                     | 128 bits                                        | 128 bits                                        | 256 bits                                        | 256 bits                                        |
+| **Nonce Length**     | 128 bits                                                              | 256 bits                                     | 128 bits                                        | 128 bits                                        | 256 bits                                        | 256 bits                                        |
+| **State Size**       | 1024 bits (8 x 128-bit blocks)                                        | 768 bits (6 x 128-bit blocks)                | 2048 bits (2 x 1024-bit states)                 | 4096 bits (4 x 1024-bit states)                 | 1536 bits (2 x 768-bit states)                  | 3072 bits (4 x 768-bit states)                  |
+| **Input Rate**       | 256 bits per update                                                   | 128 bits per update                          | 512 bits per update                             | 1024 bits per update                            | 256 bits per update                             | 512 bits per update                             |
+| **Parallelism**      | None                                                                  | None                                         | 2 parallel lanes                                | 4 parallel lanes                                | 2 parallel lanes                                | 4 parallel lanes                                |
+| **Performance**      | High on standard CPUs                                                 | High on standard CPUs                        | Higher on CPUs with AVX2                        | Higher on CPUs with AVX-512                     | Higher on CPUs with AVX2                        | Higher on CPUs with AVX-512                     |
+| **Target Use Case**  | Standard applications                                                 | Applications requiring higher security       | High-throughput applications on modern hardware | High-throughput applications on modern hardware | High-security applications with modern hardware | High-security applications with modern hardware |
+| **Security Level**   | 128-bit security                                                      | 256-bit security                             | 128-bit security                                | 128-bit security                                | 256-bit security                                | 256-bit security                                |
+| **Special Features** | Optimized for high performance on standard CPUs with AES instructions | Optimized for high security with larger keys | Parallelized version of AEGIS-128L              | Parallelized version of AEGIS-128L              | Parallelized version of AEGIS-256               | Parallelized version of AEGIS-256               |
+
 ## Installation
 
 Note that the compiler makes a difference. Zig (or a recent `clang` with target-specific options such as `-march=native`) produces more efficient code than `gcc`.