base64 decoding files of length greater than 8192? - c

Question

Whenever I try to base64 decode files (using OpenSSL's BIO_f_base64()) larger than 8192, I always seem to get some wrong value.
What is with this magic number 8192? Any help to educate me is greatly appreciated!
UPDATED:
Here is part of my code:
int dgst(char *alg)
{
EVP_MD_CTX ctx;
const EVP_MD *md;
unsigned char md_value[EVP_MAX_MD_SIZE];
unsigned int md_len, i;
char *toB64val = NULL;
char *data = NULL;
OpenSSL_add_all_digests();
md = EVP_get_digestbyname(alg);
if(!md) {
printf("Unknown message digest %s\n", alg);
exit(1);
}
data = readFileBuffer("file_out");
printf("strlen(data) %d\n", strlen(data));
EVP_MD_CTX_init(&ctx);
EVP_DigestInit_ex(&ctx, md, NULL);
EVP_DigestUpdate(&ctx, data, strlen(data));
EVP_DigestFinal_ex(&ctx, md_value, &md_len); //retrieve digest from ctx unto md_value and #bytes written is copied into md_len
EVP_MD_CTX_cleanup(&ctx);
unsigned char *copy = malloc(md_len);
memcpy(copy, md_value, md_len);
char *buff = encbase64(copy, md_len);
printf("Digest is:%s\n ", buff);
free(buff);
free(toB64val);
free(data);
return 0;
}
char *readFileBuffer(char *name)
{
FILE *file;
char *buffer = NULL;
unsigned long fileLen;
//Open file
file = fopen(name, "rb");
if (!file)
{
fprintf(stderr, "Unable to open file %s", name);
return;
}
//Get file length
fseek(file, 0, SEEK_END);
fileLen=ftell(file);
printf("file length = %ld\n", fileLen);
fseek(file, 0, SEEK_SET);
//printf("Allocate memory\n");
buffer=(char *)malloc(fileLen+1);
printf("length of write buffer = %d\n", strlen(buffer));
if (!buffer)
{
fprintf(stderr, "Memory error!");
}
long int n = fread(buffer,1, fileLen,file);
buffer[n] = '\0';
printf("Read no. of bytes = %ld into buffer \n", n);
printf("len of buffer %d \n", strlen(buffer));
if (!buffer)
{
fprintf(stderr, "Memory error!");
fclose(file);
}
fclose(file);
return buffer;
}
char *encbase64( char *input, int length)
{
BIO *bmem, *b64;
BUF_MEM *bptr;
b64 = BIO_new(BIO_f_base64());
//BIO_set_flags(b64,BIO_FLAGS_BASE64_NO_NL);
bmem = BIO_new(BIO_s_mem());
b64 = BIO_push(b64, bmem);
BIO_write(b64, input, length);
BIO_flush(b64);
BIO_get_mem_ptr(b64, &bptr);
char *buff = (char *)malloc(bptr->length);
memcpy(buff, bptr->data, bptr->length-1);
buff[bptr->length-1] = 0;
BIO_free_all(b64);
return buff;
}

Answer 1

it doesn't seem to have any problems with 8k boundaries. could you show us soucecode how you call it?
update:
int dgst(char *alg)
{
EVP_MD_CTX ctx;
const EVP_MD *md;
unsigned char md_value[EVP_MAX_MD_SIZE];
unsigned int md_len, i;
char *toB64val = NULL;
char *data = NULL;
OpenSSL_add_all_digests();
md = EVP_get_digestbyname(alg);
if(!md) {
printf("Unknown message digest %s\n", alg);
exit(1);
}
data = readFileBuffer("file_out");
//printf("strlen(data) %d\n", strlen(data)); <- don't use strlen on binary data
EVP_MD_CTX_init(&ctx);
EVP_DigestInit_ex(&ctx, md, NULL);
EVP_DigestUpdate(&ctx, data, strlen(data));
EVP_DigestFinal_ex(&ctx, md_value, &md_len); //retrieve digest from ctx unto md_value and #bytes written is copied into md_len
EVP_MD_CTX_cleanup(&ctx);
unsigned char *copy = malloc(md_len);
memcpy(copy, md_value, md_len);
char *buff = encbase64(copy, md_len);
printf("Digest is:%s\n ", buff);
free(buff);
free(toB64val);
free(data);
return 0;
}
char *readFileBuffer(char *name)
{
FILE *file;
char *buffer = NULL;
unsigned long fileLen;
//Open file
file = fopen(name, "rb");
if (!file)
{
fprintf(stderr, "Unable to open file %s", name);
return;
}
//Get file length
fseek(file, 0, SEEK_END);
fileLen=ftell(file);
printf("file length = %ld\n", fileLen);
fseek(file, 0, SEEK_SET);
//printf("Allocate memory\n");
buffer=(char *)malloc(fileLen/*+1*/); // <- not a string - no need to +1
//printf("length of write buffer = %d\n", strlen(buffer)); <- again strlen on binary data (you just allocated it, so it contains random bytes)
if (!buffer)
{
fprintf(stderr, "Memory error!");
}
long int n = fread(buffer,1, fileLen,file);
//buffer[n] = '\0'; // not a string - no need to end it
printf("Read no. of bytes = %ld into buffer \n", n);
//printf("len of buffer %d \n", strlen(buffer)); <- buffer length is in 'n'
if (!buffer)
{
fprintf(stderr, "Memory error!");
fclose(file);
}
fclose(file);
return buffer;
}
char *encbase64( char *input, int length)
{
BIO *bmem, *b64;
BUF_MEM *bptr;
b64 = BIO_new(BIO_f_base64());
//BIO_set_flags(b64,BIO_FLAGS_BASE64_NO_NL);
bmem = BIO_new(BIO_s_mem());
b64 = BIO_push(b64, bmem);
BIO_write(b64, input, length);
BIO_flush(b64);
BIO_get_mem_ptr(b64, &bptr);
char *buff = (char *)malloc(bptr->length);
memcpy(buff, bptr->data, bptr->length/*-1*/); // removed '+1'
//buff[bptr->length-1] = 0; // not a string
BIO_free_all(b64);
return buff;
}