/// <summary>
/// Try to retrieve the public key from a crypto blob.
/// </summary>
/// <remarks>
/// Can be either a PUBLICKEYBLOB or PRIVATEKEYBLOB. The BLOB must /// be unencrypted.
/// </remarks>
public unsafe static bool TryGetPublicKey(ImmutableArray <byte> blob, out ImmutableArray <byte> publicKey)
{
publicKey = ImmutableArray <byte> .Empty;
// Is this already a strong name PublicKeyBlob?
if (IsValidPublicKey(blob))
{
publicKey = blob;
return(true);
}
// Must be at least as large as header + RSA info
if (blob.Length < sizeof(BlobHeader) + sizeof(RsaPubKey))
{
return(false);
}
fixed(byte *backing = blob.DangerousGetUnderlyingArray())
{
BlobHeader *header = (BlobHeader *)backing;
RsaPubKey * rsa = (RsaPubKey *)(backing + sizeof(BlobHeader));
// The RSA magic key must match the blob id
if (header->Type == PrivateKeyBlobId &&
rsa->Magic == RSA2)
{
return(TryGetPublicKeyFromPrivateKeyBlob(backing, blob.Length, out publicKey));
}
else if (header->Type == PublicKeyBlobId &&
rsa->Magic == RSA1)
{
return(TryGetPublicKeyFromPublicKeyBlob(backing, blob.Length, out publicKey));
}
}
return(false);
}
private unsafe static bool TryGetPublicKeyFromPrivateKeyBlob(byte *blob, int blobLen, out ImmutableArray <byte> publicKey)
{
BlobHeader *header = (BlobHeader *)blob;
RsaPubKey * rsa = (RsaPubKey *)(blob + sizeof(BlobHeader));
byte version = header->Version;
uint modulusBitLength = rsa->BitLen;
uint exponent = rsa->PubExp;
byte[] modulus = new byte[modulusBitLength >> 3];
if (blobLen - s_offsetToKeyData < modulus.Length)
{
publicKey = ImmutableArray <byte> .Empty;
return(false);
}
Marshal.Copy((IntPtr)(blob + s_offsetToKeyData), modulus, 0, modulus.Length);
BlobHeader newHeader = new BlobHeader()
{
Type = PublicKeyBlobId,
Version = version,
Reserved = 0,
AlgId = AlgorithmId.RsaSign
};
RsaPubKey newRsaKey = new RsaPubKey()
{
Magic = RSA1, // Public key
BitLen = modulusBitLength,
PubExp = exponent
};
publicKey = CreateSnPublicKeyBlob(newHeader, newRsaKey, modulus);
return(true);
}