BCRYPT_RSAKEY_BLOB structure (bcrypt.h)

The BCRYPT_RSAKEY_BLOB structure is used as a header for an RSA public key or private key BLOB in memory.

Syntax

typedef struct _BCRYPT_RSAKEY_BLOB {
  ULONG Magic;
  ULONG BitLength;
  ULONG cbPublicExp;
  ULONG cbModulus;
  ULONG cbPrime1;
  ULONG cbPrime2;
} BCRYPT_RSAKEY_BLOB;

Members

Magic

Specifies the type of RSA key this BLOB represents. This can be one of the following values.

BitLength

The size, in bits, of the key.

cbPublicExp

The size, in bytes, of the exponent of the key. As of Windows 10 version 1903, public exponents larger than (2^64 - 1) are no longer supported.

cbModulus

The size, in bytes, of the modulus of the key.

cbPrime1

The size, in bytes, of the first prime number of the key. This is only used for private key BLOBs.

cbPrime2

The size, in bytes, of the second prime number of the key. This is only used for private key BLOBs.

Remarks

This structure is used as a header for a larger buffer. An RSA public key BLOB (BCRYPT_RSAPUBLIC_BLOB) has the following format in contiguous memory. All of the numbers following the structure are in big-endian format.

BCRYPT_RSAKEY_BLOB
PublicExponent[cbPublicExp] // Big-endian.
Modulus[cbModulus] // Big-endian.

An RSA private key BLOB (BCRYPT_RSAPRIVATE_BLOB) has the following format in contiguous memory. All of the numbers following the structure are in big-endian format.

BCRYPT_RSAKEY_BLOB
PublicExponent[cbPublicExp] // Big-endian.
Modulus[cbModulus] // Big-endian.
Prime1[cbPrime1] // Big-endian.
Prime2[cbPrime2] // Big-endian.

A full RSA private key BLOB (BCRYPT_RSAFULLPRIVATE_BLOB) has the following format in contiguous memory. All of the numbers following the structure are in big-endian format.

Note that in different versions of Windows, the value that PrivateExponent takes from a call of BCryptExportKey may be different as there are several mathematically equivalent representations of the PrivateExponent in cbModulus bytes. Notably, in some versions the PrivateExponent will be exported modulo (Prime1 - 1) * (Prime2 - 1), and in others it will be exported modulo LeastCommonMultiple(Prime1 - 1, Prime2 - 1).

BCRYPT_RSAKEY_BLOB
PublicExponent[cbPublicExp] // Big-endian.
Modulus[cbModulus] // Big-endian.
Prime1[cbPrime1] // Big-endian.
Prime2[cbPrime2] // Big-endian.
Exponent1[cbPrime1] // Big-endian.
Exponent2[cbPrime2] // Big-endian.
Coefficient[cbPrime1] // Big-endian.
PrivateExponent[cbModulus] // Big-endian.

Requirements

See also

BCRYPT_KEY_BLOB

BCryptExportKey

BCryptImportKey