Developers.Hash.RoundTrip

Hash to text and back again

These samples demonstrate the toString, toUrn, fromString, and fromUrn methods on the hash value objects in camper's code. They perform the following steps:

1. Compute a hash
2. Turn it into text
3. Turn it back into a hash
4. Make sure that didn't change it

When run, direct, direct2, and direct3 are always all the same.

MD5

<source lang="c"> // Takes a pointer to some memory and the number of bytes of data there // Computes the MD5 hash of the information and converts it to and from text void HashMD5(byte* p, DWORD bytes) {

// Hash the data CMD5 hash; hash.Add(p, bytes); hash.Finish(); Hashes::Md5Hash value; hash.GetHash(value);

// Turn it into text CString direct, tostring, tourn; direct = tobase16(&value[0], Hashes::Md5Hash::byteCount); tostring = value.toString(); tourn = value.toUrn();

// Turn it back into a hash value Hashes::Md5Hash value2, value3; value2.fromString(tostring); value3.fromUrn(tourn);

// Access the memory directly to confirm that didn't change it CString direct2, direct3; direct2 = tobase16(&value2[0], Hashes::Md5Hash::byteCount); direct3 = tobase16(&value3[0], Hashes::Md5Hash::byteCount); } </source>

SHA1

<source lang="c"> // Takes a pointer to some memory and the number of bytes of data there // Computes the SHA1 hash of the information and converts it to and from text void HashSHA1(byte* p, DWORD bytes) {

// Hash the data CSHA hash; hash.Add(p, bytes); hash.Finish(); Hashes::Sha1Hash value; hash.GetHash(value);

// Turn it into text CString direct, tostring, tourn; direct = tobase32(&value[0], Hashes::Sha1Hash::byteCount).MakeUpper(); tostring = value.toString(); tourn = value.toUrn();

// Turn it back into a hash value Hashes::Sha1Hash value2, value3; value2.fromString(tostring); value3.fromUrn(tourn);

// Access the memory directly to confirm that didn't change it CString direct2, direct3; direct2 = tobase32(&value2[0], Hashes::Sha1Hash::byteCount).MakeUpper(); direct3 = tobase32(&value3[0], Hashes::Sha1Hash::byteCount).MakeUpper(); } </source>

TigerTree

<source lang="c"> // Takes a pointer to some memory and the number of bytes of data there // Computes the TigerTree root hash of the information and converts it to and from text void HashTiger(byte* p, DWORD bytes) {

// Hash the data CTigerTree hash; hash.BeginFile(9, bytes); // Tree height of 9 hash.AddToFile(p, bytes); hash.FinishFile(); Hashes::TigerHash value; hash.GetRoot(value);

// Turn it into text CString direct, tostring, tourn; direct = tobase32(&value[0], Hashes::TigerHash::byteCount).MakeUpper(); tostring = value.toString(); tourn = value.toUrn();

// Turn it back into a hash value Hashes::TigerHash value2, value3; value2.fromString(tostring); value3.fromUrn(tourn);

// Access the memory directly to confirm that didn't change it CString direct2, direct3; direct2 = tobase32(&value2[0], Hashes::TigerHash::byteCount).MakeUpper(); direct3 = tobase32(&value3[0], Hashes::TigerHash::byteCount).MakeUpper(); } </source>

eDonkey2000

<source lang="c"> // Takes a pointer to some memory and the number of bytes of data there // Computes the eDonkey2000 root hash of the information and converts it to and from text void HashDonkey(byte* p, DWORD bytes) {

// Hash the data CED2K hash; hash.BeginFile(bytes); hash.AddToFile(p, bytes); hash.FinishFile(); Hashes::Ed2kHash value; hash.GetRoot(value);

// Turn it into text CString direct, tostring, tourn; direct = tobase16(&value[0], Hashes::Ed2kHash::byteCount); tostring = value.toString(); tourn = value.toUrn();

// Turn it back into a hash value Hashes::Ed2kHash value2, value3; value2.fromString(tostring); value3.fromUrn(tourn);

// Access the memory directly to confirm that didn't change it CString direct2, direct3; direct2 = tobase16(&value2[0], Hashes::Ed2kHash::byteCount); direct3 = tobase16(&value3[0], Hashes::Ed2kHash::byteCount); } </source>

Questions

• What about MD4?
• These objects all have a toShortUrn method, but there is no corresponding fromShortUrn