adding the encryption file with the new branch

encryption.c

@@ -0,0 +1,148 @@
+#include <openssl/conf.h>
+#include <openssl/evp.h>
+#include <openssl/err.h>
+#include <string.h>
+#include "ppm.h"
+int main (void)
+{
+    /*
+     * Set up the key and iv. Do I need to say to not hard code these in a
+     * real application? :-)
+     */
+
+    /* A 256 bit key */
+    unsigned char *key = (unsigned char *)"01234567890123456789012345678901";
+
+    /* A 128 bit IV */
+    unsigned char *iv = (unsigned char *)"0123456789012345";
+    /* Message to be encrypted */
+    unsigned char *plaintext =(unsigned char *)malloc(sizeof(unsigned char)*100);
+    printf("enter the message-> ");
+    scanf("%s",plaintext);
+    /*
+     * Buffer for ciphertext. Ensure the buffer is long enough for the
+     * ciphertext which may be longer than the plaintext, depending on the
+     * algorithm and mode.
+     */
+    unsigned char ciphertext[128];
+
+    /* Buffer for the decrypted text */
+    unsigned char decryptedtext[128];
+
+    int decryptedtext_len, ciphertext_len;
+
+    /* Encrypt the plaintext */
+    ciphertext_len = encrypt (plaintext, strlen ((char *)plaintext), key, iv,
+                              ciphertext);
+
+    /* Do something useful with the ciphertext here */
+    printf("Ciphertext is:\n");
+    BIO_dump_fp (stdout, (const char *)ciphertext, ciphertext_len);
+
+    /* Decrypt the ciphertext */
+    decryptedtext_len = decrypt(ciphertext, ciphertext_len, key, iv,
+                                decryptedtext);
+
+    /* Add a NULL terminator. We are expecting printable text */
+    decryptedtext[decryptedtext_len] = '\0';
+
+    /* Show the decrypted text */
+    printf("Decrypted text is:\n");
+    printf("%s\n", decryptedtext);
+
+
+    return 0;
+}
+void handleErrors(void)
+{
+    ERR_print_errors_fp(stderr);
+    abort();
+}
+int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
+            unsigned char *iv, unsigned char *ciphertext)
+{
+    EVP_CIPHER_CTX *ctx;
+
+    int len;
+
+    int ciphertext_len;
+
+    /* Create and initialise the context */
+    if(!(ctx = EVP_CIPHER_CTX_new()))
+        handleErrors();
+
+    /*
+     * Initialise the encryption operation. IMPORTANT - ensure you use a key
+     * and IV size appropriate for your cipher
+     * In this example we are using 256 bit AES (i.e. a 256 bit key). The
+     * IV size for *most* modes is the same as the block size. For AES this
+     * is 128 bits
+     */
+    if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
+        handleErrors();
+
+    /*
+     * Provide the message to be encrypted, and obtain the encrypted output.
+     * EVP_EncryptUpdate can be called multiple times if necessary
+     */
+    if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
+        handleErrors();
+    ciphertext_len = len;
+
+    /*
+     * Finalise the encryption. Further ciphertext bytes may be written at
+     * this stage.
+     */
+    if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
+        handleErrors();
+    ciphertext_len += len;
+
+    /* Clean up */
+    EVP_CIPHER_CTX_free(ctx);
+
+    return ciphertext_len;
+}
+int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
+            unsigned char *iv, unsigned char *plaintext)
+{
+    EVP_CIPHER_CTX *ctx;
+
+    int len;
+
+    int plaintext_len;
+
+    /* Create and initialise the context */
+    if(!(ctx = EVP_CIPHER_CTX_new()))
+        handleErrors();
+
+    /*
+     * Initialise the decryption operation. IMPORTANT - ensure you use a key
+     * and IV size appropriate for your cipher
+     * In this example we are using 256 bit AES (i.e. a 256 bit key). The
+     * IV size for *most* modes is the same as the block size. For AES this
+     * is 128 bits
+     */
+    if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
+        handleErrors();
+
+    /*
+     * Provide the message to be decrypted, and obtain the plaintext output.
+     * EVP_DecryptUpdate can be called multiple times if necessary.
+     */
+    if(1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
+        handleErrors();
+    plaintext_len = len;
+
+    /*
+     * Finalise the decryption. Further plaintext bytes may be written at
+     * this stage.
+     */
+    if(1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len))
+        handleErrors();
+    plaintext_len += len;
+
+    /* Clean up */
+    EVP_CIPHER_CTX_free(ctx);
+
+    return plaintext_len;
+}