I have a function that writes encryption of msg to filename using key
and iv. I have another function that reads filename and decrypts msg
using key and iv.
If I run my encrypt function to create the encrypted file, and then
try and decrypt later with my decrypt function, I get this:
error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad
decrypt:evp_enc.c:461:
If, however, I run my encrypt and decrypt functions back to back, the
decryption works. I think it's a block length or padding checking
problem, but can't figure out why it works sometimes.
i.e. this works:
bf_encrypt( "test.bf", "Test msg", "Test key","12345678" );
cout << bf_decrypt( "test.bf", "Test key","12345678" ) << endl;
And this doesn't:
// bf_encrypt( "test.bf", "Test msg", "Test key","12345678" );
cout << bf_decrypt( "test.bf", "Test key","12345678" ) << endl;
Charles
int bf_encrypt( string filename, string msg, string key, string iv ) {
unsigned char outbuf[1024];
int outlen, tmplen;
EVP_CIPHER_CTX ctx;
EVP_CIPHER_CTX_init( &ctx );
EVP_EncryptInit_ex( &ctx, EVP_bf_cbc(), NULL, (const unsigned
char*)key.c_str(), (const unsigned char*)iv.c_str() );
if( !EVP_EncryptUpdate( &ctx, outbuf, &outlen, (const unsigned
char*)msg.c_str(), msg.length() ) ) {
/* Error */
return 0;
}
if( !EVP_EncryptFinal_ex(&ctx, outbuf + outlen, &tmplen) ) {
/* Error */
return 0;
}
outlen += tmplen;
EVP_CIPHER_CTX_cleanup(&ctx);
ofstream out( filename.c_str(), ios::out | ios::binary );
if( !out ) {
cout << "Cannot open file.\n";
return 0;
}
else {
out.write((char *) &outbuf, outlen );
out.close();
}
return 1;
}
std::string bf_decrypt( std::string filename, std::string key,
std::string iv ) {
unsigned char outbuf[1024];
int outlen, tmplen;
ifstream file ( filename.c_str(), ios::in|ios::binary|ios::ate );
if ( file.is_open() ) {
ifstream::pos_type size;
char * memblock;
size = file.tellg();
memblock = new char [size];
file.seekg ( 0, ios::beg );
file.read ( memblock, size );
file.close();
EVP_CIPHER_CTX ctx;
EVP_CIPHER_CTX_init( &ctx );
EVP_DecryptInit_ex( &ctx, EVP_bf_cbc(), NULL, (const unsigned
char*)key.c_str(), (const unsigned char*)iv.c_str() );
if( !EVP_DecryptUpdate( &ctx, outbuf, &outlen, (const unsigned
char*)memblock, size ) ) {
cerr << "Error in EVP_DecryptUpdate" << endl;
return 0;
}
if( !EVP_DecryptFinal_ex( &ctx, outbuf + outlen, &tmplen ) ) {
cerr << "Error in EVP_DecryptFinal_ex:" << endl;
ERR_load_crypto_strings();
BIO * bo = BIO_new_fp( stdout, BIO_NOCLOSE );
ERR_print_errors( bo );
exit( 2 );
}
outlen += tmplen;
EVP_CIPHER_CTX_cleanup( &ctx );
delete[] memblock;
std::string result ( reinterpret_cast<const char*>(outbuf),
outlen );
return result;
}
else {
cerr << "Unable to open file";
return "";
}
}
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