btcd: github.com/btcsuite/btcd/btcec Index | Examples | Files

package btcec

import "github.com/btcsuite/btcd/btcec"

Package btcec implements support for the elliptic curves needed for bitcoin.

Bitcoin uses elliptic curve cryptography using koblitz curves (specifically secp256k1) for cryptographic functions. See http://www.secg.org/collateral/sec2_final.pdf for details on the standard.

This package provides the data structures and functions implementing the crypto/elliptic Curve interface in order to permit using these curves with the standard crypto/ecdsa package provided with go. Helper functionality is provided to parse signatures and public keys from standard formats. It was designed for use with btcd, but should be general enough for other uses of elliptic curve crypto. It was originally based on some initial work by ThePiachu, but has significantly diverged since then.

This example demonstrates decrypting a message using a private key that is first parsed from raw bytes.

Code:

// Decode the hex-encoded private key.
pkBytes, err := hex.DecodeString("a11b0a4e1a132305652ee7a8eb7848f6ad" +
    "5ea381e3ce20a2c086a2e388230811")
if err != nil {
    fmt.Println(err)
    return
}

privKey, _ := btcec.PrivKeyFromBytes(btcec.S256(), pkBytes)

ciphertext, err := hex.DecodeString("35f644fbfb208bc71e57684c3c8b437402ca" +
    "002047a2f1b38aa1a8f1d5121778378414f708fe13ebf7b4a7bb74407288c1958969" +
    "00207cf4ac6057406e40f79961c973309a892732ae7a74ee96cd89823913b8b8d650" +
    "a44166dc61ea1c419d47077b748a9c06b8d57af72deb2819d98a9d503efc59fc8307" +
    "d14174f8b83354fac3ff56075162")

// Try decrypting the message.
plaintext, err := btcec.Decrypt(privKey, ciphertext)
if err != nil {
    fmt.Println(err)
    return
}

fmt.Println(string(plaintext))

Output:

test message

This example demonstrates encrypting a message for a public key that is first parsed from raw bytes, then decrypting it using the corresponding private key.

Code:

// Decode the hex-encoded pubkey of the recipient.
pubKeyBytes, err := hex.DecodeString("04115c42e757b2efb7671c578530ec191a1" +
    "359381e6a71127a9d37c486fd30dae57e76dc58f693bd7e7010358ce6b165e483a29" +
    "21010db67ac11b1b51b651953d2") // uncompressed pubkey
if err != nil {
    fmt.Println(err)
    return
}
pubKey, err := btcec.ParsePubKey(pubKeyBytes, btcec.S256())
if err != nil {
    fmt.Println(err)
    return
}

// Encrypt a message decryptable by the private key corresponding to pubKey
message := "test message"
ciphertext, err := btcec.Encrypt(pubKey, []byte(message))
if err != nil {
    fmt.Println(err)
    return
}

// Decode the hex-encoded private key.
pkBytes, err := hex.DecodeString("a11b0a4e1a132305652ee7a8eb7848f6ad" +
    "5ea381e3ce20a2c086a2e388230811")
if err != nil {
    fmt.Println(err)
    return
}
// note that we already have corresponding pubKey
privKey, _ := btcec.PrivKeyFromBytes(btcec.S256(), pkBytes)

// Try decrypting and verify if it's the same message.
plaintext, err := btcec.Decrypt(privKey, ciphertext)
if err != nil {
    fmt.Println(err)
    return
}

fmt.Println(string(plaintext))

Output:

test message

This example demonstrates signing a message with a secp256k1 private key that is first parsed form raw bytes and serializing the generated signature.

Code:

// Decode a hex-encoded private key.
pkBytes, err := hex.DecodeString("22a47fa09a223f2aa079edf85a7c2d4f87" +
    "20ee63e502ee2869afab7de234b80c")
if err != nil {
    fmt.Println(err)
    return
}
privKey, pubKey := btcec.PrivKeyFromBytes(btcec.S256(), pkBytes)

// Sign a message using the private key.
message := "test message"
messageHash := chainhash.DoubleHashB([]byte(message))
signature, err := privKey.Sign(messageHash)
if err != nil {
    fmt.Println(err)
    return
}

// Serialize and display the signature.
fmt.Printf("Serialized Signature: %x\n", signature.Serialize())

// Verify the signature for the message using the public key.
verified := signature.Verify(messageHash, pubKey)
fmt.Printf("Signature Verified? %v\n", verified)

Output:

Serialized Signature: 304402201008e236fa8cd0f25df4482dddbb622e8a8b26ef0ba731719458de3ccd93805b022032f8ebe514ba5f672466eba334639282616bb3c2f0ab09998037513d1f9e3d6d
Signature Verified? true

This example demonstrates verifying a secp256k1 signature against a public key that is first parsed from raw bytes. The signature is also parsed from raw bytes.

Code:

// Decode hex-encoded serialized public key.
pubKeyBytes, err := hex.DecodeString("02a673638cb9587cb68ea08dbef685c" +
    "6f2d2a751a8b3c6f2a7e9a4999e6e4bfaf5")
if err != nil {
    fmt.Println(err)
    return
}
pubKey, err := btcec.ParsePubKey(pubKeyBytes, btcec.S256())
if err != nil {
    fmt.Println(err)
    return
}

// Decode hex-encoded serialized signature.
sigBytes, err := hex.DecodeString("30450220090ebfb3690a0ff115bb1b38b" +
    "8b323a667b7653454f1bccb06d4bbdca42c2079022100ec95778b51e707" +
    "1cb1205f8bde9af6592fc978b0452dafe599481c46d6b2e479")

if err != nil {
    fmt.Println(err)
    return
}
signature, err := btcec.ParseSignature(sigBytes, btcec.S256())
if err != nil {
    fmt.Println(err)
    return
}

// Verify the signature for the message using the public key.
message := "test message"
messageHash := chainhash.DoubleHashB([]byte(message))
verified := signature.Verify(messageHash, pubKey)
fmt.Println("Signature Verified?", verified)

Output:

Signature Verified? true

Index

Examples

Package Files

btcec.go ciphering.go doc.go field.go precompute.go privkey.go pubkey.go secp256k1.go signature.go

Constants

const (
    PubKeyBytesLenCompressed   = 33
    PubKeyBytesLenUncompressed = 65
    PubKeyBytesLenHybrid       = 65
)

These constants define the lengths of serialized public keys.

const MinSigLen = 8

MinSigLen is the minimum length of a DER encoded signature and is when both R and S are 1 byte each. 0x30 + <1-byte> + 0x02 + 0x01 + <byte> + 0x2 + 0x01 + <byte>

const PrivKeyBytesLen = 32

PrivKeyBytesLen defines the length in bytes of a serialized private key.

Variables

var (
    // ErrInvalidMAC occurs when Message Authentication Check (MAC) fails
    // during decryption. This happens because of either invalid private key or
    // corrupt ciphertext.
    ErrInvalidMAC = errors.New("invalid mac hash")
)

func Decrypt Uses

func Decrypt(priv *PrivateKey, in []byte) ([]byte, error)

Decrypt decrypts data that was encrypted using the Encrypt function.

func Encrypt Uses

func Encrypt(pubkey *PublicKey, in []byte) ([]byte, error)

Encrypt encrypts data for the target public key using AES-256-CBC. It also generates a private key (the pubkey of which is also in the output). The only supported curve is secp256k1. The `structure' that it encodes everything into is:

struct {
	// Initialization Vector used for AES-256-CBC
	IV [16]byte
	// Public Key: curve(2) + len_of_pubkeyX(2) + pubkeyX +
	// len_of_pubkeyY(2) + pubkeyY (curve = 714)
	PublicKey [70]byte
	// Cipher text
	Data []byte
	// HMAC-SHA-256 Message Authentication Code
	HMAC [32]byte
}

The primary aim is to ensure byte compatibility with Pyelliptic. Also, refer to section 5.8.1 of ANSI X9.63 for rationale on this format.

func GenerateSharedSecret Uses

func GenerateSharedSecret(privkey *PrivateKey, pubkey *PublicKey) []byte

GenerateSharedSecret generates a shared secret based on a private key and a public key using Diffie-Hellman key exchange (ECDH) (RFC 4753). RFC5903 Section 9 states we should only return x.

func IsCompressedPubKey Uses

func IsCompressedPubKey(pubKey []byte) bool

IsCompressedPubKey returns true the the passed serialized public key has been encoded in compressed format, and false otherwise.

func NAF Uses

func NAF(k []byte) ([]byte, []byte)

NAF takes a positive integer k and returns the Non-Adjacent Form (NAF) as two byte slices. The first is where 1s will be. The second is where -1s will be. NAF is convenient in that on average, only 1/3rd of its values are non-zero. This is algorithm 3.30 from [GECC].

Essentially, this makes it possible to minimize the number of operations since the resulting ints returned will be at least 50% 0s.

func PrivKeyFromBytes Uses

func PrivKeyFromBytes(curve elliptic.Curve, pk []byte) (*PrivateKey,
    *PublicKey)

PrivKeyFromBytes returns a private and public key for `curve' based on the private key passed as an argument as a byte slice.

func SignCompact Uses

func SignCompact(curve *KoblitzCurve, key *PrivateKey,
    hash []byte, isCompressedKey bool) ([]byte, error)

SignCompact produces a compact signature of the data in hash with the given private key on the given koblitz curve. The isCompressed parameter should be used to detail if the given signature should reference a compressed public key or not. If successful the bytes of the compact signature will be returned in the format: <(byte of 27+public key solution)+4 if compressed >< padded bytes for signature R><padded bytes for signature S> where the R and S parameters are padde up to the bitlengh of the curve.

type KoblitzCurve Uses

type KoblitzCurve struct {
    *elliptic.CurveParams

    H   int // cofactor of the curve.
    // contains filtered or unexported fields
}

KoblitzCurve supports a koblitz curve implementation that fits the ECC Curve interface from crypto/elliptic.

func S256 Uses

func S256() *KoblitzCurve

S256 returns a Curve which implements secp256k1.

func (*KoblitzCurve) Add Uses

func (curve *KoblitzCurve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int)

Add returns the sum of (x1,y1) and (x2,y2). Part of the elliptic.Curve interface.

func (*KoblitzCurve) Double Uses

func (curve *KoblitzCurve) Double(x1, y1 *big.Int) (*big.Int, *big.Int)

Double returns 2*(x1,y1). Part of the elliptic.Curve interface.

func (*KoblitzCurve) IsOnCurve Uses

func (curve *KoblitzCurve) IsOnCurve(x, y *big.Int) bool

IsOnCurve returns boolean if the point (x,y) is on the curve. Part of the elliptic.Curve interface. This function differs from the crypto/elliptic algorithm since a = 0 not -3.

func (*KoblitzCurve) Params Uses

func (curve *KoblitzCurve) Params() *elliptic.CurveParams

Params returns the parameters for the curve.

func (*KoblitzCurve) Q Uses

func (curve *KoblitzCurve) Q() *big.Int

Q returns the (P+1)/4 constant for the curve for use in calculating square roots via exponentiation.

func (*KoblitzCurve) QPlus1Div4 Uses

func (curve *KoblitzCurve) QPlus1Div4() *big.Int

QPlus1Div4 returns the (P+1)/4 constant for the curve for use in calculating square roots via exponentiation.

DEPRECATED: The actual value returned is (P+1)/4, where as the original method name implies that this value is (((P+1)/4)+1)/4. This method is kept to maintain backwards compatibility of the API. Use Q() instead.

func (*KoblitzCurve) ScalarBaseMult Uses

func (curve *KoblitzCurve) ScalarBaseMult(k []byte) (*big.Int, *big.Int)

ScalarBaseMult returns k*G where G is the base point of the group and k is a big endian integer. Part of the elliptic.Curve interface.

func (*KoblitzCurve) ScalarMult Uses

func (curve *KoblitzCurve) ScalarMult(Bx, By *big.Int, k []byte) (*big.Int, *big.Int)

ScalarMult returns k*(Bx, By) where k is a big endian integer. Part of the elliptic.Curve interface.

type PrivateKey Uses

type PrivateKey ecdsa.PrivateKey

PrivateKey wraps an ecdsa.PrivateKey as a convenience mainly for signing things with the the private key without having to directly import the ecdsa package.

func NewPrivateKey Uses

func NewPrivateKey(curve elliptic.Curve) (*PrivateKey, error)

NewPrivateKey is a wrapper for ecdsa.GenerateKey that returns a PrivateKey instead of the normal ecdsa.PrivateKey.

func (*PrivateKey) PubKey Uses

func (p *PrivateKey) PubKey() *PublicKey

PubKey returns the PublicKey corresponding to this private key.

func (*PrivateKey) Serialize Uses

func (p *PrivateKey) Serialize() []byte

Serialize returns the private key number d as a big-endian binary-encoded number, padded to a length of 32 bytes.

func (*PrivateKey) Sign Uses

func (p *PrivateKey) Sign(hash []byte) (*Signature, error)

Sign generates an ECDSA signature for the provided hash (which should be the result of hashing a larger message) using the private key. Produced signature is deterministic (same message and same key yield the same signature) and canonical in accordance with RFC6979 and BIP0062.

func (*PrivateKey) ToECDSA Uses

func (p *PrivateKey) ToECDSA() *ecdsa.PrivateKey

ToECDSA returns the private key as a *ecdsa.PrivateKey.

type PublicKey Uses

type PublicKey ecdsa.PublicKey

PublicKey is an ecdsa.PublicKey with additional functions to serialize in uncompressed, compressed, and hybrid formats.

func ParsePubKey Uses

func ParsePubKey(pubKeyStr []byte, curve *KoblitzCurve) (key *PublicKey, err error)

ParsePubKey parses a public key for a koblitz curve from a bytestring into a ecdsa.Publickey, verifying that it is valid. It supports compressed, uncompressed and hybrid signature formats.

func RecoverCompact Uses

func RecoverCompact(curve *KoblitzCurve, signature,
    hash []byte) (*PublicKey, bool, error)

RecoverCompact verifies the compact signature "signature" of "hash" for the Koblitz curve in "curve". If the signature matches then the recovered public key will be returned as well as a boolen if the original key was compressed or not, else an error will be returned.

func (*PublicKey) IsEqual Uses

func (p *PublicKey) IsEqual(otherPubKey *PublicKey) bool

IsEqual compares this PublicKey instance to the one passed, returning true if both PublicKeys are equivalent. A PublicKey is equivalent to another, if they both have the same X and Y coordinate.

func (*PublicKey) SerializeCompressed Uses

func (p *PublicKey) SerializeCompressed() []byte

SerializeCompressed serializes a public key in a 33-byte compressed format.

func (*PublicKey) SerializeHybrid Uses

func (p *PublicKey) SerializeHybrid() []byte

SerializeHybrid serializes a public key in a 65-byte hybrid format.

func (*PublicKey) SerializeUncompressed Uses

func (p *PublicKey) SerializeUncompressed() []byte

SerializeUncompressed serializes a public key in a 65-byte uncompressed format.

func (*PublicKey) ToECDSA Uses

func (p *PublicKey) ToECDSA() *ecdsa.PublicKey

ToECDSA returns the public key as a *ecdsa.PublicKey.

type Signature Uses

type Signature struct {
    R   *big.Int
    S   *big.Int
}

Signature is a type representing an ecdsa signature.

func ParseDERSignature Uses

func ParseDERSignature(sigStr []byte, curve elliptic.Curve) (*Signature, error)

ParseDERSignature parses a signature in DER format for the curve type `curve` into a Signature type. If parsing according to the less strict BER format is needed, use ParseSignature.

func ParseSignature Uses

func ParseSignature(sigStr []byte, curve elliptic.Curve) (*Signature, error)

ParseSignature parses a signature in BER format for the curve type `curve' into a Signature type, perfoming some basic sanity checks. If parsing according to the more strict DER format is needed, use ParseDERSignature.

func (*Signature) IsEqual Uses

func (sig *Signature) IsEqual(otherSig *Signature) bool

IsEqual compares this Signature instance to the one passed, returning true if both Signatures are equivalent. A signature is equivalent to another, if they both have the same scalar value for R and S.

func (*Signature) Serialize Uses

func (sig *Signature) Serialize() []byte

Serialize returns the ECDSA signature in the more strict DER format. Note that the serialized bytes returned do not include the appended hash type used in Bitcoin signature scripts.

encoding/asn1 is broken so we hand roll this output:

0x30 <length> 0x02 <length r> r 0x02 <length s> s

func (*Signature) Verify Uses

func (sig *Signature) Verify(hash []byte, pubKey *PublicKey) bool

Verify calls ecdsa.Verify to verify the signature of hash using the public key. It returns true if the signature is valid, false otherwise.

Package btcec imports 21 packages (graph) and is imported by 859 packages. Updated 2019-10-11. Refresh now. Tools for package owners.