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November 17, 2015 13:04
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openssl RSA demo
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| #include <openssl/rsa.h> | |
| #include <openssl/pem.h> | |
| #include <openssl/err.h> | |
| #include <stdio.h> | |
| #include <string.h> | |
| #define KEY_LENGTH 2048 | |
| #define PUB_EXP 3 | |
| #define PRINT_KEYS | |
| #define WRITE_TO_FILE | |
| int main(void) { | |
| size_t pri_len; // Length of private key | |
| size_t pub_len; // Length of public key | |
| char *pri_key; // Private key | |
| char *pub_key; // Public key | |
| char msg[KEY_LENGTH/8]; // Message to encrypt | |
| char *encrypt = NULL; // Encrypted message | |
| char *decrypt = NULL; // Decrypted message | |
| char *err; // Buffer for any error messages | |
| // Generate key pair | |
| printf("Generating RSA (%d bits) keypair...", KEY_LENGTH); | |
| fflush(stdout); | |
| RSA *keypair = RSA_generate_key(KEY_LENGTH, PUB_EXP, NULL, NULL); | |
| // To get the C-string PEM form: | |
| BIO *pri = BIO_new(BIO_s_mem()); | |
| BIO *pub = BIO_new(BIO_s_mem()); | |
| PEM_write_bio_RSAPrivateKey(pri, keypair, NULL, NULL, 0, NULL, NULL); | |
| PEM_write_bio_RSAPublicKey(pub, keypair); | |
| pri_len = BIO_pending(pri); | |
| pub_len = BIO_pending(pub); | |
| pri_key = malloc(pri_len + 1); | |
| pub_key = malloc(pub_len + 1); | |
| BIO_read(pri, pri_key, pri_len); | |
| BIO_read(pub, pub_key, pub_len); | |
| pri_key[pri_len] = '\0'; | |
| pub_key[pub_len] = '\0'; | |
| #ifdef PRINT_KEYS | |
| printf("\n%s\n%s\n", pri_key, pub_key); | |
| #endif | |
| printf("done.\n"); | |
| // Get the message to encrypt | |
| printf("Message to encrypt: "); | |
| fgets(msg, KEY_LENGTH-1, stdin); | |
| msg[strlen(msg)-1] = '\0'; | |
| // Encrypt the message | |
| encrypt = malloc(RSA_size(keypair)); | |
| int encrypt_len; | |
| err = malloc(130); | |
| if((encrypt_len = RSA_public_encrypt(strlen(msg)+1, (unsigned char*)msg, (unsigned char*)encrypt, | |
| keypair, RSA_PKCS1_OAEP_PADDING)) == -1) { | |
| ERR_load_crypto_strings(); | |
| ERR_error_string(ERR_get_error(), err); | |
| fprintf(stderr, "Error encrypting message: %s\n", err); | |
| goto free_stuff; | |
| } | |
| #ifdef WRITE_TO_FILE | |
| // Write the encrypted message to a file | |
| FILE *out = fopen("out.bin", "w"); | |
| fwrite(encrypt, sizeof(*encrypt), RSA_size(keypair), out); | |
| fclose(out); | |
| printf("Encrypted message written to file.\n"); | |
| free(encrypt); | |
| encrypt = NULL; | |
| // Read it back | |
| printf("Reading back encrypted message and attempting decryption...\n"); | |
| encrypt = malloc(RSA_size(keypair)); | |
| out = fopen("out.bin", "r"); | |
| fread(encrypt, sizeof(*encrypt), RSA_size(keypair), out); | |
| fclose(out); | |
| #endif | |
| // Decrypt it | |
| decrypt = malloc(encrypt_len); | |
| if(RSA_private_decrypt(encrypt_len, (unsigned char*)encrypt, (unsigned char*)decrypt, | |
| keypair, RSA_PKCS1_OAEP_PADDING) == -1) { | |
| ERR_load_crypto_strings(); | |
| ERR_error_string(ERR_get_error(), err); | |
| fprintf(stderr, "Error decrypting message: %s\n", err); | |
| goto free_stuff; | |
| } | |
| printf("Decrypted message: %s\n", decrypt); | |
| free_stuff: | |
| RSA_free(keypair); | |
| BIO_free_all(pub); | |
| BIO_free_all(pri); | |
| free(pri_key); | |
| free(pub_key); | |
| free(encrypt); | |
| free(decrypt); | |
| free(err); | |
| return 0; | |
| } |
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origin
https://shanetully.com/2012/04/simple-public-key-encryption-with-rsa-and-openssl/