TripleDESCryptoServiceProvider.Blocksize different from PHP's mcrypt_get_key_size

Question

why does (C#)

System.Security.Cryptography.TripleDESCryptoServiceProvider.BlockSize

and (PHP)

mcrypt_get_block_size(MCRYPT_TIPRLEDES, MCRYPT_MODE_ECB);

returns a different result?

Answer 1

The C# System.Security.Cryptography.TripleDESCryptoServiceProvider.BlockSize value is in bits , while PHP's mcrypt_get_block_size() returns it in bytes .

1 byte = 8 bits; 64 / 8 = 8 bytes

It's the same value, just represented in different measurement units.

Answer 2

1. Encryption key sizes and block sizes are not related.

2. DES and thus Triple DES have a block size of 8-bytes.

3. Triple DES has a key size of 168-bits in 24-bytes. There are schemes to use shorter keys such as 16-bytes and duplicate the first 8-bytes to the last 8-bytes, this sometimes called Two Key Triple DES.