可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试):
问题:
What I am trying to do: Write a program in C that opens a file of arbitrary size and reads its contents. Once The contents are read it will encrypt them in AES 256 CBC and save the ciphertext to a file called ciphertext. Once this is saved it will close both files. Then will open the cipher text from the file that was just saved and decrypt the cipher text and save it to a file called decrypted.
My Problem: It seems to never decrypt my cipher text. I get garbage, I have no idea what I am doing wrong. Please help.
#include #include #include #include #include void encrypt(FILE *ifp, FILE *ofp) { //Get file size fseek(ifp, 0L, SEEK_END); int fsize = ftell(ifp); //set back to normal fseek(ifp, 0L, SEEK_SET); int outLen1 = 0; int outLen2 = 0; unsigned char *indata = malloc(fsize); unsigned char *outdata = malloc(fsize*2); unsigned char ckey[] = "thiskeyisverybad"; unsigned char ivec[] = "dontusethisinput"; //Read File fread(indata,sizeof(char),fsize, ifp);//Read Entire File //Set up encryption EVP_CIPHER_CTX ctx; EVP_EncryptInit(&ctx,EVP_aes_256_cbc(),ckey,ivec); EVP_EncryptUpdate(&ctx,outdata,&outLen1,indata,fsize); EVP_EncryptFinal(&ctx,outdata,&outLen2); fwrite(outdata,sizeof(char),fsize,ofp); } void decrypt(FILE *ifp, FILE *ofp) { //Get file size fseek(ifp, 0L, SEEK_END); int fsize = ftell(ifp); //set back to normal fseek(ifp, 0L, SEEK_SET); int outLen1 = 0; int outLen2 = 0; unsigned char *indata = malloc(fsize); unsigned char *outdata = malloc(fsize*2); unsigned char ckey[] = "thiskeyisverybad"; unsigned char ivec[] = "dontusethisinput"; //Read File fread(indata,sizeof(char),fsize, ifp);//Read Entire File //setup decryption EVP_CIPHER_CTX ctx; EVP_DecryptInit(&ctx,EVP_aes_256_cbc(),ckey,ivec); EVP_DecryptUpdate(&ctx,outdata,&outLen1,indata,fsize); EVP_DecryptFinal(&ctx,outdata,&outLen2); fwrite(outdata,sizeof(char),fsize,ofp); } int main(int argc, char *argv[]) { FILE *fIN, *fOUT; fIN = fopen("plain.txt", "rb");//File to be encrypted; plain text fOUT = fopen("cyphertext.txt", "wb");//File to be written; cipher text encrypt(fIN, fOUT); fclose(fIN); fclose(fOUT); //Decrypt file now fIN = fopen("cyphertext.txt", "rb");//File to be written; cipher text fOUT = fopen("decrypted.txt", "wb");//File to be written; cipher text decrypt(fIN,fOUT); fclose(fIN); fclose(fOUT); return 0; }
Note: there may be some misspellings. EDIT: Seems Like I made a mistake with the key and IV, both of which are 128 bit and I am trying to use the 256 bit CBC. This was my problem, seems to work once I changed it to
EVP_aes_128_cbc()
回答1:
Here is my version of your code. Naturally I like it better, but I offer it just as an alternative. Note the complete absence of error checking: real code would have it.
#include #include #include #include #include #ifndef TRUE #define TRUE 1 #endif #ifndef FALSE #define FALSE 0 #endif /** * Encrypt or decrypt, depending on flag 'should_encrypt' */ void en_de_crypt(int should_encrypt, FILE *ifp, FILE *ofp, unsigned char *ckey, unsigned char *ivec) { const unsigned BUFSIZE=4096; unsigned char *read_buf = malloc(BUFSIZE); unsigned char *cipher_buf; unsigned blocksize; int out_len; EVP_CIPHER_CTX ctx; EVP_CipherInit(&ctx, EVP_aes_256_cbc(), ckey, ivec, should_encrypt); blocksize = EVP_CIPHER_CTX_block_size(&ctx); cipher_buf = malloc(BUFSIZE + blocksize); while (1) { // Read in data in blocks until EOF. Update the ciphering with each read. int numRead = fread(read_buf, sizeof(unsigned char), BUFSIZE, ifp); EVP_CipherUpdate(&ctx, cipher_buf, &out_len, read_buf, numRead); fwrite(cipher_buf, sizeof(unsigned char), out_len, ofp); if (numRead /path/to/file/exe"); return -1; } // First encrypt the file fIN = fopen("plain.txt", "rb"); //File to be encrypted; plain text fOUT = fopen("cyphertext.txt", "wb"); //File to be written; cipher text en_de_crypt(TRUE, fIN, fOUT, ckey, ivec); fclose(fIN); fclose(fOUT); //Decrypt file now fIN = fopen("cyphertext.txt", "rb"); //File to be read; cipher text fOUT = fopen("decrypted.txt", "wb"); //File to be written; cipher text en_de_crypt(FALSE, fIN, fOUT, ckey, ivec); fclose(fIN); fclose(fOUT); return 0; }
回答2:
This code works, if anyone has some suggestions as to how it would be cleaner or more efficient please drop a comment.
#include #include #include #include #include void encrypt(FILE *ifp, FILE *ofp) { //Get file size fseek(ifp, 0L, SEEK_END); int fsize = ftell(ifp); //set back to normal fseek(ifp, 0L, SEEK_SET); int outLen1 = 0; int outLen2 = 0; unsigned char *indata = malloc(fsize); unsigned char *outdata = malloc(fsize*2); unsigned char ckey[] = "thiskeyisverybad"; unsigned char ivec[] = "dontusethisinput"; //Read File fread(indata,sizeof(char),fsize, ifp);//Read Entire File //Set up encryption EVP_CIPHER_CTX ctx; EVP_EncryptInit(&ctx,EVP_aes_128_cbc(),ckey,ivec); EVP_EncryptUpdate(&ctx,outdata,&outLen1,indata,fsize); EVP_EncryptFinal(&ctx,outdata + outLen1,&outLen2); fwrite(outdata,sizeof(char),outLen1 + outLen2,ofp); } void decrypt(FILE *ifp, FILE *ofp) { //Get file size fseek(ifp, 0L, SEEK_END); int fsize = ftell(ifp); //set back to normal fseek(ifp, 0L, SEEK_SET); int outLen1 = 0; int outLen2 = 0; unsigned char *indata = malloc(fsize); unsigned char *outdata = malloc(fsize); unsigned char ckey[] = "thiskeyisverybad"; unsigned char ivec[] = "dontusethisinput"; //Read File fread(indata,sizeof(char),fsize, ifp);//Read Entire File //setup decryption EVP_CIPHER_CTX ctx; EVP_DecryptInit(&ctx,EVP_aes_128_cbc(),ckey,ivec); EVP_DecryptUpdate(&ctx,outdata,&outLen1,indata,fsize); EVP_DecryptFinal(&ctx,outdata + outLen1,&outLen2); fwrite(outdata,sizeof(char),outLen1 + outLen2,ofp); } int main(int argc, char *argv[]) { if(argc != 2){ printf("Usage: /path/to/file/exe"); return -1; } FILE *fIN, *fOUT; fIN = fopen("plain.txt", "rb");//File to be encrypted; plain text fOUT = fopen("cyphertext.txt", "wb");//File to be written; cipher text encrypt(fIN, fOUT); fclose(fIN); fclose(fOUT); //Decrypt file now fIN = fopen("cyphertext.txt", "rb");//File to be written; cipher text fOUT = fopen("decrypted.txt", "wb");//File to be written; cipher text decrypt(fIN,fOUT); fclose(fIN); fclose(fOUT); return 0; }
Also According to this post the EVP api will handle an arbitrary sized input
AES Encryption- large files
