Private Key Blob Format - Win32 Programmer's Reference (win32.hlp)

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Private Key Blob Format

Private key blobs (type PRIVATEKEYBLOB) are used to store RSA public/private key pairs. They have the following format:

BLOBHEADER blobheader;

RSAPUBKEY rsapubkey;

BYTE modulus[rsapubkey.bitlen/8];

BYTE prime1[rsapubkey.bitlen/16];

BYTE prime2[rsapubkey.bitlen/16];

BYTE exponent1[rsapubkey.bitlen/16];

BYTE exponent2[rsapubkey.bitlen/16];

BYTE coefficient[rsapubkey.bitlen/16];

BYTE privateExponent[rsapubkey.bitlen/8];

If the key blob is encrypted, then everything but the BLOBHEADER portion of the blob is encrypted. Note that the encryption algorithm and encryption key parameters are not stored along with the private key blob. It is the responsibility of the application to manage this information.

The following table describes each private key blob component. Note that these fields largely correspond to the ones described in section 7.2 of PKCS #1: RSA Encryption Standard.

Field	Description
blobheader	A BLOBHEADER structure as described in a previous section. The bType field must always have a value of PRIVATEKEYBLOB.
rsapubkey	A RSAPUBKEY structure as described in a previous section. The magic field must always have a value of 0x32415352 ("RSA2").
modulus	The modulus. This has a value of "prime1 * prime2" and is often known as "n".
prime1	Prime number 1, often known as "p".
prime2	Prime number 2, often known as "q".
exponent1	Exponent 1. This has a numeric value of "d mod (p - 1)".
exponent2	Exponent 2. This has a numeric value of "d mod (q - 1)".
coefficient	Coefficient. This has a numeric value of "(inverse of q) mod p".
privateExponent	Private exponent, often known as "d".

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