Salt Value Functionality
The Base Provider creates 40-bit symmetric keys created with eleven bytes of zero-value salt, eleven bytes of nonzero salt if CRYPT_CREATE_SALT is specified, or no salt value. A 40-bit symmetric key with zero-value salt, however, is not equivalent to a 40-bit symmetric key without salt. For interoperability, keys must be created without salt. This problem results from a default condition that occurs only with keys of exactly 40 bits. All other key lengths do not have salt allocated by default.
Both the Base Providers and the Extended Provider can use the CRYPT_NO_SALT flag to specify that no salt value is allocated for a 40-bit symmetric key. The functions that accept this flag are CryptGenKey, CryptDeriveKey, and CryptImportKey. By default, these functions provide backward compatibility for the 40-bit symmetric key case by continuing the use of the eleven-byte-long zero-value salt.