Re: CryptExport private key only

From: Michel Gallant (neutron_at_nspxistar.ca)
Date: 10/26/03 

Date: Sun, 26 Oct 2003 11:38:16 -0500

"Anatoly" <wiretransfers@yahoo.com> wrote in message news:eHO88H4mDHA.3612@TK2MSFTNGP11.phx.gbl...
> do I understand correctly, that when using RSA public/private key pair
> encryption, CryptExport's PRIVATEKEYBLOB flag will export both private and
> public keys together?

Yes, that is correct:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/security/security/private_key_blobs.asp

> from conventional use of Public/Private key pairs, it seems that one is
> supposed to use the public key to encrypt data and private key to always
> decrypt data.

With RSA asymmetric cipher supports encrypting limited amount of data
(a hash or a secret key) with one key and decrypting with the other key:

 (1) using public key to encrypt is typically used to encrypt a secret session key
 to a recipient whose public key/certificate you have
 (2) you can use your private key to encrypt a hash (your digital signature)
  or you can use your private key to decrypt something encrypted as in (1)

> Is it legitimate to interchange the private/public keys in their purpose?
> that is can I use the public key to decrypt and private to encrypt and
> benefit from the same level of protection as the conventional scenario?
 See comments above

 - Michel Gallant
    Visual Security MVP

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