Class CoseEcPublicKey

Namespace

Yubico.YubiKey.Fido2.Cose

Assembly

Yubico.YubiKey.dll

A representation of an Elliptic Curve public key in COSE form.

public class CoseEcPublicKey : CoseKey

Inheritance

object

CoseKey

CoseEcPublicKey

Inherited Members

CoseKey.TagKeyType

CoseKey.TagAlgorithm

CoseKey.Type

CoseKey.Algorithm

CoseKey.Create(ReadOnlyMemory<byte>, out int)

Remarks

An ECC public key consists of a curve and public point. In FIDO2, the curve is represented by the CoseAlgorithmIdentifier and the public point is simply an x-coordinate and a y-coordinate.

The FIDO2 standard also specifies an encoding of the public key information. It uses the representation defined in RFC8152: CBOR Object Signing and Encryption (COSE) standard. Supplementary information can be found in section 6.5.6 of the CTAP2.1 specification (under the heading `getPublicKey()`).

This class has multiple constructors. One constructs an empty object and allows the caller to set the key parameters via the properties on this class. Another constructs a key based on the COSE form encoded in CBOR. Lastly, there is a constructor that takes in a .NET representation of an EC public key used for interoperating with the .NET cryptographic library.

The YubiKey's FIDO2 application currently only supports the NIST P-256 curve. Thus, the SDK - as of version 1.5.0 - will also only support this curve.

Constructors

CoseEcPublicKey(ReadOnlyMemory<byte>)

Construct a CoseEcPublicKey based on the CBOR encoding of a COSE_Key.

public CoseEcPublicKey(ReadOnlyMemory<byte> encodedCoseKey)

Parameters

encodedCoseKey ReadOnlyMemory<byte>

The CBOR encoding.

Exceptions

Ctap2DataException

The encodedCoseKey is not a correct EC Public Key encoding.

CoseEcPublicKey(ECParameters)

Construct a CoseEcPublicKey based on .NET elliptic curve parameters.

public CoseEcPublicKey(ECParameters ecParameters)

Parameters

ecParameters ECParameters

An ECParameters structure with a specified Curve and a public point Q.

Exceptions

ArgumentException

The ECParameters object does not contain a valid curve and

NotSupportedException

The parameters/public key specified is not supported.

CoseEcPublicKey(CoseEcCurve, ReadOnlyMemory<byte>, ReadOnlyMemory<byte>)

Construct a CoseEcPublicKey based on the curve and point.

public CoseEcPublicKey(CoseEcCurve curve, ReadOnlyMemory<byte> xCoordinate, ReadOnlyMemory<byte> yCoordinate)

Parameters

curve CoseEcCurve

The curve for this public key.

xCoordinate ReadOnlyMemory<byte>

The x-coordinate of the public point.

yCoordinate ReadOnlyMemory<byte>

The y-coordinate of the public point.

Remarks

An ECC public key is a curve and public point (x and y coordinates). This constructor expects the length of each coordinate to be at least one byte and 32 bytes or fewer. Valid keys are P-256, P-384, and P-521. Note: Certain keys might not be supported by the YubiKey.

Exceptions

ArgumentException

The xCoordinate or yCoordinate is not the correct length, or when the curve is not supported.

CoseEcPublicKey(CoseEcCurve, CoseAlgorithmIdentifier, ReadOnlyMemory<byte>, ReadOnlyMemory<byte>)

Construct a CoseEcPublicKey based on the curve and x and y coordinates.

public CoseEcPublicKey(CoseEcCurve curve, CoseAlgorithmIdentifier algorithm, ReadOnlyMemory<byte> xCoordinate, ReadOnlyMemory<byte> yCoordinate)

Parameters

curve CoseEcCurve

The curve for this public key.

algorithm CoseAlgorithmIdentifier

The algorithm of the key.

xCoordinate ReadOnlyMemory<byte>

The x-coordinate of the public point.

yCoordinate ReadOnlyMemory<byte>

The y-coordinate of the public point.

Remarks

An ECC public key is a curve and public point (x and y coordinates). Valid keys are P-256, P-384, and P-521. Note: Certain keys might not be supported by the YubiKey.

Exceptions

ArgumentException

The xCoordinate or yCoordinate is not the correct length, or when the curve is not supported.

Properties

Curve

The Elliptic Curve that the key resides on.

public CoseEcCurve Curve { get; set; }

Property Value

CoseEcCurve

Exceptions

NotSupportedException

On set, the curve specified is not supported.

XCoordinate

The X-coordinate of the public point.

public ReadOnlyMemory<byte> XCoordinate { get; set; }

Property Value

ReadOnlyMemory<byte>

Exceptions

ArgumentException

On set, the coordinate in not the correct length.

YCoordinate

The Y-coordinate of the public point.

public ReadOnlyMemory<byte> YCoordinate { get; set; }

Property Value

ReadOnlyMemory<byte>

Exceptions

ArgumentException

On set, the coordinate in not the correct length.

Methods

CreateFromEncodedKey(ReadOnlyMemory<byte>)

Creates a new instance of CoseEcPublicKey from the given encoded COSE key.

public static CoseEcPublicKey CreateFromEncodedKey(ReadOnlyMemory<byte> encodedCoseKey)

Parameters

encodedCoseKey ReadOnlyMemory<byte>

The encoded COSE key in CBOR format.

Returns

CoseEcPublicKey

A CoseEcPublicKey object initialized with the provided encoded key data.

Exceptions

Ctap2DataException

Thrown if the encodedCoseKey is not a valid EC Public Key encoding.

Encode()

Return a new byte array that is the key data encoded following the FIDO2/CBOR standard.

public override byte[] Encode()

Returns

byte[]

The encoded key.

Exceptions

InvalidOperationException

The object contains no key data.

ToEcParameters()

Returns the COSE key as a new .NET ECParameters structure. Used for interoperating with the .NET crypto library.

public ECParameters ToEcParameters()

Returns

ECParameters

The public key in the form of an ECParameters structure.