# Package ecdh

## Overview ▸

## Index ▸

## type Curve ¶ 1.20

type Curve interface { // GenerateKey generates a random PrivateKey. // // Most applications should use [crypto/rand.Reader] as rand. Note that the // returned key does not depend deterministically on the bytes read from rand, // and may change between calls and/or between versions. GenerateKey(rand io.Reader) (*PrivateKey, error) // NewPrivateKey checks that key is valid and returns a PrivateKey. // // For NIST curves, this follows SEC 1, Version 2.0, Section 2.3.6, which // amounts to decoding the bytes as a fixed length big endian integer and // checking that the result is lower than the order of the curve. The zero // private key is also rejected, as the encoding of the corresponding public // key would be irregular. // // For X25519, this only checks the scalar length. NewPrivateKey(key []byte) (*PrivateKey, error) // NewPublicKey checks that key is valid and returns a PublicKey. // // For NIST curves, this decodes an uncompressed point according to SEC 1, // Version 2.0, Section 2.3.4. Compressed encodings and the point at // infinity are rejected. // // For X25519, this only checks the u-coordinate length. Adversarially // selected public keys can cause ECDH to return an error. NewPublicKey(key []byte) (*PublicKey, error) // contains filtered or unexported methods }

### func P256 ¶ 1.20

func P256() Curve

P256 returns a Curve which implements NIST P-256 (FIPS 186-3, section D.2.3), also known as secp256r1 or prime256v1.

Multiple invocations of this function will return the same value, which can be used for equality checks and switch statements.

### func P384 ¶ 1.20

func P384() Curve

P384 returns a Curve which implements NIST P-384 (FIPS 186-3, section D.2.4), also known as secp384r1.

Multiple invocations of this function will return the same value, which can be used for equality checks and switch statements.

### func P521 ¶ 1.20

func P521() Curve

P521 returns a Curve which implements NIST P-521 (FIPS 186-3, section D.2.5), also known as secp521r1.

Multiple invocations of this function will return the same value, which can be used for equality checks and switch statements.

### func X25519 ¶ 1.20

func X25519() Curve

X25519 returns a Curve which implements the X25519 function over Curve25519 (RFC 7748, Section 5).

Multiple invocations of this function will return the same value, so it can be used for equality checks and switch statements.

## type PrivateKey ¶ 1.20

PrivateKey is an ECDH private key, usually kept secret.

These keys can be parsed with crypto/x509.ParsePKCS8PrivateKey and encoded with crypto/x509.MarshalPKCS8PrivateKey. For NIST curves, they then need to be converted with crypto/ecdsa.PrivateKey.ECDH after parsing.

```
type PrivateKey struct {
// contains filtered or unexported fields
}
```

### func (*PrivateKey) Bytes ¶ 1.20

func (k *PrivateKey) Bytes() []byte

Bytes returns a copy of the encoding of the private key.

### func (*PrivateKey) Curve ¶ 1.20

func (k *PrivateKey) Curve() Curve

### func (*PrivateKey) ECDH ¶ 1.20

func (k *PrivateKey) ECDH(remote *PublicKey) ([]byte, error)

ECDH performs an ECDH exchange and returns the shared secret. The PrivateKey and PublicKey must use the same curve.

For NIST curves, this performs ECDH as specified in SEC 1, Version 2.0, Section 3.3.1, and returns the x-coordinate encoded according to SEC 1, Version 2.0, Section 2.3.5. The result is never the point at infinity.

For X25519, this performs ECDH as specified in RFC 7748, Section 6.1. If the result is the all-zero value, ECDH returns an error.

### func (*PrivateKey) Equal ¶ 1.20

func (k *PrivateKey) Equal(x crypto.PrivateKey) bool

Equal returns whether x represents the same private key as k.

Note that there can be equivalent private keys with different encodings which would return false from this check but behave the same way as inputs to [ECDH].

This check is performed in constant time as long as the key types and their curve match.

### func (*PrivateKey) Public ¶ 1.20

func (k *PrivateKey) Public() crypto.PublicKey

Public implements the implicit interface of all standard library private keys. See the docs of crypto.PrivateKey.

### func (*PrivateKey) PublicKey ¶ 1.20

func (k *PrivateKey) PublicKey() *PublicKey

## type PublicKey ¶ 1.20

PublicKey is an ECDH public key, usually a peer's ECDH share sent over the wire.

These keys can be parsed with crypto/x509.ParsePKIXPublicKey and encoded with crypto/x509.MarshalPKIXPublicKey. For NIST curves, they then need to be converted with crypto/ecdsa.PublicKey.ECDH after parsing.

```
type PublicKey struct {
// contains filtered or unexported fields
}
```

### func (*PublicKey) Bytes ¶ 1.20

func (k *PublicKey) Bytes() []byte

Bytes returns a copy of the encoding of the public key.

### func (*PublicKey) Curve ¶ 1.20

func (k *PublicKey) Curve() Curve

### func (*PublicKey) Equal ¶ 1.20

func (k *PublicKey) Equal(x crypto.PublicKey) bool

Equal returns whether x represents the same public key as k.

Note that there can be equivalent public keys with different encodings which would return false from this check but behave the same way as inputs to ECDH.

This check is performed in constant time as long as the key types and their curve match.