Security options for encrypted private keys

Private keys are stored by default in a PKCS-8 encrypted format, protected by a password. The default algorithm is "pbeWithSHAAnd3-KeyTripleDES-CBC" from PKCS-5.

The approximate ranking for the encryption schemes in increasing order of security is

1. "pbeWithMD2AndDES-CBC"
2. "pbeWithMD5AndDES-CBC"
3. "pbeWithSHA1AndDES-CBC"
4. ...big gap!...
5. "pbeWithSHAAnd3-KeyTripleDES-CBC" (default)
6. "pkcs5PBES2" + "des-EDE3-CBC"
7. "pkcs5PBES2" + "AES128-CBC"
8. "pkcs5PBES2" + "AES192-CBC"
9. "pkcs5PBES2" + "AES256-CBC"

The less-secure algorithms pbeWithxxxAndDES-CBC using single DES are provided just in case you need compatibility with an older system. Do not use them unless you have to.

The PBES2 scheme uses the PKCS-5 PBKDF2 key derivation function with hmacWithSHA1 as the default psuedo-random function (PRF). To use a stronger message digest function from the SHA-2 family in the PRF, add one of the following options

1. PKI_HASH_SHA224 for hmacWithSHA224
2. PKI_HASH_SHA256 for hmacWithSHA256
3. PKI_HASH_SHA384 for hmacWithSHA384
4. PKI_HASH_SHA512 for hmacWithSHA512

So, for example, to specify using PBES2 with AES256-CBC-Pad as the block cipher and HMAC-with-SHA256 as the PRF, use

	
Dim nOptions As Long
nOptions = PKI_PBE_PBES2 + PKI_BC_AES256 + PKI_HASH_SHA512

Remember that the security of all these schemes is limited by the strength of the password used. Also, other systems may not necessarily support all the alternatives provided here.

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