## Documentation ¶

### Overview ¶

Package ecdsa implements the Elliptic Curve Digital Signature Algorithm, as defined in FIPS 186-4 and SEC 1, Version 2.0.

Signatures generated by this package are not deterministic, but entropy is mixed with the private key and the message, achieving the same level of security in case of randomness source failure.

Operations involving private keys are implemented using constant-time algorithms, as long as an elliptic.Curve returned by elliptic.P224, elliptic.P256, elliptic.P384, or elliptic.P521 is used.

## Example ¶

package main import ( "crypto/ecdsa" "crypto/elliptic" "crypto/rand" "crypto/sha256" "fmt" ) func main() { privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader) if err != nil { panic(err) } msg := "hello, world" hash := sha256.Sum256([]byte(msg)) sig, err := ecdsa.SignASN1(rand.Reader, privateKey, hash[:]) if err != nil { panic(err) } fmt.Printf("signature: %x\n", sig) valid := ecdsa.VerifyASN1(&privateKey.PublicKey, hash[:], sig) fmt.Println("signature verified:", valid) }

```
Output:
```

### Index ¶

- func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error)
- func SignASN1(rand io.Reader, priv *PrivateKey, hash []byte) ([]byte, error)
- func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool
- func VerifyASN1(pub *PublicKey, hash, sig []byte) bool
- type PrivateKey
- type PublicKey

#### Examples ¶

### Constants ¶

This section is empty.

### Variables ¶

This section is empty.

### Functions ¶

#### func Sign ¶

Sign signs a hash (which should be the result of hashing a larger message) using the private key, priv. If the hash is longer than the bit-length of the private key's curve order, the hash will be truncated to that length. It returns the signature as a pair of integers. Most applications should use SignASN1 instead of dealing directly with r, s.

#### func SignASN1 ¶ added in go1.15

SignASN1 signs a hash (which should be the result of hashing a larger message) using the private key, priv. If the hash is longer than the bit-length of the private key's curve order, the hash will be truncated to that length. It returns the ASN.1 encoded signature.

The signature is randomized. Most applications should use crypto/rand.Reader as rand. Note that the returned signature does not depend deterministically on the bytes read from rand, and may change between calls and/or between versions.

#### func Verify ¶

Verify verifies the signature in r, s of hash using the public key, pub. Its return value records whether the signature is valid. Most applications should use VerifyASN1 instead of dealing directly with r, s.

The inputs are not considered confidential, and may leak through timing side channels, or if an attacker has control of part of the inputs.

#### func VerifyASN1 ¶ added in go1.15

VerifyASN1 verifies the ASN.1 encoded signature, sig, of hash using the public key, pub. Its return value records whether the signature is valid.

The inputs are not considered confidential, and may leak through timing side channels, or if an attacker has control of part of the inputs.

### Types ¶

#### type PrivateKey ¶

PrivateKey represents an ECDSA private key.

#### func GenerateKey ¶

GenerateKey generates a new ECDSA private key for the specified curve.

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.

#### func (*PrivateKey) ECDH ¶ added in go1.20

func (k *PrivateKey) ECDH() (*ecdh.PrivateKey, error)

ECDH returns k as a ecdh.PrivateKey. It returns an error if the key is invalid according to the definition of ecdh.Curve.NewPrivateKey, or if the Curve is not supported by crypto/ecdh.

#### func (*PrivateKey) Equal ¶ added in go1.15

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

Equal reports whether priv and x have the same value.

See PublicKey.Equal for details on how Curve is compared.

#### func (*PrivateKey) Public ¶ added in go1.4

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

Public returns the public key corresponding to priv.

#### func (*PrivateKey) Sign ¶ added in go1.4

func (priv *PrivateKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error)

Sign signs digest with priv, reading randomness from rand. The opts argument is not currently used but, in keeping with the crypto.Signer interface, should be the hash function used to digest the message.

This method implements crypto.Signer, which is an interface to support keys where the private part is kept in, for example, a hardware module. Common uses can use the SignASN1 function in this package directly.

#### type PublicKey ¶

PublicKey represents an ECDSA public key.

#### func (*PublicKey) ECDH ¶ added in go1.20

ECDH returns k as a ecdh.PublicKey. It returns an error if the key is invalid according to the definition of ecdh.Curve.NewPublicKey, or if the Curve is not supported by crypto/ecdh.

#### func (*PublicKey) Equal ¶ added in go1.15

Equal reports whether pub and x have the same value.

Two keys are only considered to have the same value if they have the same Curve value. Note that for example elliptic.P256 and elliptic.P256().Params() are different values, as the latter is a generic not constant time implementation.