SHA2
Documentation |
#include <cryptopp/sha.h>
|
SHA2 is the Secure Hash Standard and specified in FIPS 180-4. The standard provides SHA2-224, SHA2-256, SHA2-384 and SHA2-512. Crypto++ provides all hashes from FIPS 180-4.
All Crypto++ hashes derive from HashTransformation
. The base class provides functions like Update
, Final
and Verify
. You can swap-in any hash for any other hash in your program.
Sample Programs
There are five sample programs. The first prints information about the hash. The second creates a hash using SHA-256 class. The third creates a hash using a pipeline. The fourth and filth examples show how to verify an existing digest.
The examples below use SHA-256, but you can swap-in any hash function, like PanamaHash or SM3.
The first example dumps the name, digest size and internal block size of the hash.
#include "cryptlib.h" #include "sha.h" #include <iostream> int main (int argc, char* argv[]) { using namespace CryptoPP; SHA256 hash; std::cout << "Name: " << hash.AlgorithmName() << std::endl; std::cout << "Digest size: " << hash.DigestSize() << std::endl; std::cout << "Block size: " << hash.BlockSize() << std::endl; return 0; }
Running the program results in the following. In general you should use DigestSize
and avoid BlockSize
. BlockSize
is usually not required by a program.
$ ./test.exe Name: SHA-256 Digest size: 32 Block size: 64
The second example creates a hash using the hash object and member functions. You add data using Update
and you calculate the hash using Final
. Calling Final
resets the hash so you don't need to do it manually.
using namespace CryptoPP; HexEncoder encoder(new FileSink(std::cout)); std::string msg = "Yoda said, Do or do not. There is no try."; std::string digest; SHA256 hash; hash.Update((const byte*)msg.data(), msg.size()); digest.resize(hash.DigestSize()); hash.Final((byte*)&digest[0]); std::cout << "Message: " << msg << std::endl; std::cout << "Digest: "; StringSource(digest, true, new Redirector(encoder)); std::cout << std::endl;
Running the program results in the following.
$ ./test.exe Message: Yoda said, Do or do not. There is no try. Digest: F00E3F70A268FBA990296B32FF2B6CE7A0757F31EC3059B13D3DB1E60D9E885C
You can also obtain a truncated hash rather than the full hash using TruncatedFinal
.
std::cout << "Message: " << msg << std::endl; hash.Update((const byte*)msg.data(), msg.size()); digest.resize(hash.DigestSize()/2); hash.TruncatedFinal((byte*)&digest[0], digest.size()); std::cout << "Digest: "; StringSource(digest, true, new Redirector(encoder)); std::cout << std::endl;
The program produces the following result.
$ ./test.exe Message: Yoda said, Do or do not. There is no try. Digest: F00E3F70A268FBA990296B32FF2B6CE7
Using a pipeline produces the same result. It relieves you of calling Update
and Final manually. The code also uses a HashFilter
, which has its own wiki page at HashFilter.
std::string msg = "Yoda said, Do or do not. There is no try."; std::string digest; StringSource(msg, true, new HashFilter(hash, new StringSink(digest))); std::cout << "Message: " << msg << std::endl; std::cout << "Digest: "; StringSource(digest, true, new Redirector(encoder)); std::cout << std::endl;
Running the program results in the following.
$ ./test.exe Message: Yoda said, Do or do not. There is no try. Digest: F00E3F70A268FBA990296B32FF2B6CE7A0757F31EC3059B13D3DB1E60D9E885C
The fourth program verifies an existing hash using the hash object. Notice the program proceeds as if the hash is going to be calculated. But rather than calling Final
to retrieve the hash, Verify
is called to verify the existing hash.
SHA256 hash; hash.Update((const byte*)msg.data(), msg.size()); bool verified = hash.Verify((const byte*)digest.data()); if (verified == true) std::cout << "Verified hash over message" << std::endl; else std::cout << "Failed to verify hash over message" << std::endl;
The final program verifies an existing hash using a pipeline. The code uses a HashVerificationFilter
, which has its own wiki page at HashVerificationFilter.
bool result; StringSource(digest+msg, true, new HashVerificationFilter(hash, new ArraySink((byte*)&result, sizeof(result)))); if (result == true) std::cout << "Verified hash over message" << std::endl; else std::cout << "Failed to verify hash over message" << std::endl;
Running the program results in the following output.
$ ./test.exe Message: Yoda said, Do or do not. There is no try. Digest: F00E3F70A268FBA990296B32FF2B6CE7A0757F31EC3059B13D3DB1E60D9E885C Verified hash over message
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