• Definition: Nettle is a low-level cryptographic library that provides a wide range of cryptographic algorithms. It is designed to be easy to use, flexible, and efficient, making it suitable for a variety of applications.
• Function: Provides the building blocks for implementing cryptographic protocols, including encryption, decryption, hashing, and digital signatures.
• Components:

   * '''Symmetric Key Algorithms''': Includes AES, DES, and Camellia.
   * '''Hash Functions''': Includes SHA-1, SHA-256, SHA-512, MD5, and others.
   * '''Public Key Algorithms''': Includes RSA, DSA, and ECDSA.
   * '''Message Authentication Codes (MACs)''': Includes HMAC and CMAC.
   * '''Random Number Generation''': Provides cryptographically secure random number generation.

• Features:

   * '''Performance''': Optimized for performance, suitable for use in high-throughput applications.
   * '''Flexibility''': Offers a wide range of cryptographic primitives that can be combined in various ways.
   * '''Portability''': Designed to be portable across different operating systems and architectures.
   * '''Interoperability''': Compatible with other cryptographic libraries and standards.

• Usage: Used in various security applications, including secure communications, data protection, and digital signatures.

• Encrypting data with AES using Nettle in C:

   ```c
   #include 
   #include 

 void aes_encrypt_example() {
     struct aes_ctx ctx;
     uint8_t key[16] = "mysecretkey12345"; // 128-bit key
     uint8_t plaintext[16] = "exampleplaintext";
     uint8_t ciphertext[16];

     // Initialize AES context with the key
     aes_set_encrypt_key(&ctx, sizeof(key), key);

     // Encrypt the plaintext
     aes_encrypt(&ctx, sizeof(plaintext), ciphertext, plaintext);

     // Print the ciphertext
     for (int i = 0; i < sizeof(ciphertext); i++) {
         printf("%02x", ciphertext[i]);
     }
     printf("\n");
 }

 int main() {
     aes_encrypt_example();
     return 0;
 }
 ```

• Hashing data with SHA-256 using Nettle in Python (using a ctypes wrapper):

   ```python
   import ctypes
   import ctypes.util

 # Load the Nettle library
 nettle = ctypes.CDLL(ctypes.util.find_library('nettle'))

 # Define the SHA-256 context structure
 class Sha256Ctx(ctypes.Structure):
     _fields_ = [("state", ctypes.c_uint32 * 8),
                 ("count", ctypes.c_uint64),
                 ("block", ctypes.c_uint8 * 64),
                 ("index", ctypes.c_size_t)]

 # Initialize the SHA-256 context
 ctx = Sha256Ctx()
 nettle.nettle_sha256_init(ctypes.byref(ctx))

 # Update the context with the input data
 data = b"hello world"
 nettle.nettle_sha256_update(ctypes.byref(ctx), ctypes.c_size_t(len(data)), data)

 # Finalize the hash and retrieve the output
 digest = (ctypes.c_uint8 * 32)()
 nettle.nettle_sha256_digest(ctypes.byref(ctx), ctypes.c_size_t(len(digest)), digest)

 # Print the SHA-256 hash
 print("SHA-256:", "".join("{:02x}".format(b) for b in digest))
 ```

• Nettle: A low-level cryptographic library that provides a wide range of cryptographic algorithms, including symmetric key algorithms, hash functions, public key algorithms, message authentication codes, and random number generation. It is designed for performance, flexibility, and portability, making it suitable for various security applications. Examples in C and Python demonstrate encryption with AES and hashing with SHA-256.