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  1. PO
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    <p>The error is in the way the EVP_DecryptFinal and EVP_EncryptFinal are called. These functions should be called in the end of the for cycle, also the final part where to olen is added tlen and written again was duplicating output. Below is the final working version:</p> <pre><code>#include &lt;openssl/blowfish.h&gt; #include &lt;openssl/evp.h&gt; #include &lt;fcntl.h&gt; #include &lt;stdio.h&gt; #include &lt;sys/stat.h&gt; #include &lt;sys/types.h&gt; #include &lt;unistd.h&gt; #include &lt;string.h&gt; #define IP_SIZE 1024 #define OP_SIZE 1024 + EVP_MAX_BLOCK_LENGTH unsigned char key[16]; unsigned char iv[8]; int generate_key() { int i, fd; if ((fd = open("/dev/random", O_RDONLY)) == -1) perror("open error"); if ((read(fd, key, 16)) == -1) perror("read key error"); if ((read(fd, iv, 8)) == -1) perror("read iv error"); printf("128 bit key:\n"); for (i = 0; i &lt; 16; i++) printf("%4d ", key[i]); printf("\nInitialization vector\n"); for (i = 0; i &lt; 8; i++) printf("%4d ", iv[i]); printf("\n"); close(fd); return 0; } int do_decrypt(int infd, int outfd) { unsigned char *inbuff, *outbuf; int olen=0, tlen=0, n=0; EVP_CIPHER_CTX ctx; EVP_CIPHER_CTX_init(&amp;ctx); EVP_DecryptInit(&amp;ctx, EVP_bf_cbc(), key, iv); outbuf = (unsigned char *) malloc(sizeof(unsigned char) * OP_SIZE); inbuff = (unsigned char *) malloc(sizeof(unsigned char) * IP_SIZE); /* keep reading until a break */ for (;;) { memset(inbuff, 0, IP_SIZE); if ((n = read(infd, inbuff, IP_SIZE)) == -1) { perror("read error"); break; } else if (n == 0) break; memset(outbuf, 0, OP_SIZE); if (EVP_DecryptUpdate(&amp;ctx, outbuf, &amp;olen, inbuff, n) != 1) { printf("error in decrypt update\n"); return 0; } if ((n = write(outfd, outbuf, olen)) == -1) perror("write error"); } tlen=0; if (EVP_DecryptFinal(&amp;ctx, outbuf + olen, &amp;tlen) != 1) { perror("error in decrypt final"); return 0; } if ((n = write(outfd, outbuf+olen, tlen)) == -1) perror("write error"); EVP_CIPHER_CTX_cleanup(&amp;ctx); return 1; } int do_encrypt(int infd, int outfd) { unsigned char *inbuff, *outbuf; int olen=0, tlen=0, n=0; EVP_CIPHER_CTX ctx; EVP_CIPHER_CTX_init(&amp;ctx); EVP_EncryptInit(&amp;ctx, EVP_bf_cbc(), key, iv); outbuf = (unsigned char *) malloc(sizeof(unsigned char) * OP_SIZE); inbuff = (unsigned char *) malloc(sizeof(unsigned char) * IP_SIZE); for (;;) { memset(inbuff, 0, IP_SIZE); if ((n = read(infd, inbuff, IP_SIZE)) == -1) { perror("read error"); break; } else if (n == 0) break; if (EVP_EncryptUpdate(&amp;ctx, outbuf, &amp;olen, inbuff, n) != 1) { printf("error in encrypt update\n"); return 0; } if ((n = write(outfd, outbuf, olen)) == -1) perror("write error"); } tlen=0; if (EVP_EncryptFinal(&amp;ctx, outbuf + olen, &amp;tlen) != 1) { printf("error in encrypt final\n"); return 0; } if ((n = write(outfd, outbuf+olen, tlen)) == -1) perror("write error"); EVP_CIPHER_CTX_cleanup(&amp;ctx); return 1; } int main(int argc, char *argv[]) { int flags1 = 0, flags2 = 0, outfd, infd; mode_t mode; memset(key, 0, 16); memset(iv, 0, 8); memset(&amp;mode, 0, sizeof(mode)); flags1 = flags1 | O_RDONLY; flags2 = flags2 | O_RDONLY; flags2 = flags2 | O_WRONLY; flags2 = flags2 | O_CREAT; mode = mode | S_IRUSR; mode = mode | S_IWUSR; generate_key(); if ((infd = open(argv[1], flags1, mode)) == -1) perror("open input file error"); if ((outfd = open(argv[2], flags2, mode)) == -1) perror("open output file error"); do_encrypt(infd, outfd); close(infd); fsync(outfd); close(outfd); if ((infd = open(argv[2], flags1, mode)) == -1) perror("open output file error"); if ((outfd = open(argv[3], flags2, mode)) == -1) perror("open output file error"); do_decrypt(infd, outfd); close(infd); fsync(infd); close(outfd); return 0; } </code></pre>
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    1. POAssistance with openssl blowfish simple example inserting garbage characters
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    1. COI seriously have my doubts about that. If this were true the last number of bits would we written out twice.
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    2. COFrom my understanding of the block cyphers this makes sense. The *Final functions are used for the last bits of data that are not multiple of the block size. Besides, the fact that you are doing a *Final function call inside the loop is the cause of the garbage characters in the decrypted file. In my test this solved the problem
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    3. COmy previous answer was not completely right. The last edit is a complete working version, based on the code in your question (with the fixes and some cleanups).
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