106 lines
3.3 KiB
Go
106 lines
3.3 KiB
Go
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// cryptopasta - basic cryptography examples
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//
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// Written in 2015 by George Tankersley <george.tankersley@gmail.com>
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//
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// To the extent possible under law, the author(s) have dedicated all copyright
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// and related and neighboring rights to this software to the public domain
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// worldwide. This software is distributed without any warranty.
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//
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// You should have received a copy of the CC0 Public Domain Dedication along
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// with this software. If not, see // <http://creativecommons.org/publicdomain/zero/1.0/>.
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// Provides message authentication and asymmetric signatures.
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//
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// Message authentication: HMAC SHA512/256
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// This is a slight twist on the highly dependable HMAC-SHA256 that gains
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// performance on 64-bit systems and consistency with our hashing
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// recommendation.
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//
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// Asymmetric Signature: ECDSA using P256 and SHA256
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// ECDSA is the best compromise between cryptographic concerns and support for
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// our internal use cases (e.g. RFC7518). The Go standard library
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// implementation has some protection against entropy problems, but is not
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// deterministic. See
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// https://github.com/golang/go/commit/8d7bf2291b095d3a2ecaa2609e1101be46d80deb
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package cryptopasta
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import (
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"crypto/ecdsa"
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"crypto/elliptic"
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"crypto/hmac"
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"crypto/rand"
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"crypto/sha256"
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"crypto/sha512"
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"io"
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"math/big"
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)
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// NewHMACKey generates a random 256-bit secret key for HMAC use.
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// Because key generation is critical, it panics if the source of randomness fails.
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func NewHMACKey() *[32]byte {
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key := &[32]byte{}
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_, err := io.ReadFull(rand.Reader, key[:])
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if err != nil {
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panic(err)
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}
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return key
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}
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// GenerateHMAC produces a symmetric signature using a shared secret key.
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func GenerateHMAC(data []byte, key *[32]byte) []byte {
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h := hmac.New(sha512.New512_256, key[:])
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h.Write(data)
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return h.Sum(nil)
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}
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// CheckHMAC securely checks the supplied MAC against a message using the shared secret key.
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func CheckHMAC(data, suppliedMAC []byte, key *[32]byte) bool {
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expectedMAC := GenerateHMAC(data, key)
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return hmac.Equal(expectedMAC, suppliedMAC)
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}
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// GenerateSigningKey generates a random P-256 ECDSA private key.
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func NewSigningKey() (*ecdsa.PrivateKey, error) {
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key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
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return key, err
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}
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// Sign signs arbitrary data using ECDSA.
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func Sign(data []byte, privkey *ecdsa.PrivateKey) ([]byte, error) {
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// hash message
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digest := sha256.Sum256(data)
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// sign the hash
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r, s, err := ecdsa.Sign(rand.Reader, privkey, digest[:])
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if err != nil {
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return nil, err
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}
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// encode the signature {R, S}
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// big.Int.Bytes() will need padding in the case of leading zero bytes
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params := privkey.Curve.Params()
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curveOrderByteSize := params.P.BitLen() / 8
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rBytes, sBytes := r.Bytes(), s.Bytes()
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signature := make([]byte, curveOrderByteSize*2)
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copy(signature[curveOrderByteSize-len(rBytes):], rBytes)
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copy(signature[curveOrderByteSize*2-len(sBytes):], sBytes)
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return signature, nil
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}
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// Verify checks a raw ECDSA signature.
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// Returns true if it's valid and false if not.
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func Verify(data, signature []byte, pubkey *ecdsa.PublicKey) bool {
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// hash message
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digest := sha256.Sum256(data)
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curveOrderByteSize := pubkey.Curve.Params().P.BitLen() / 8
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r, s := new(big.Int), new(big.Int)
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r.SetBytes(signature[:curveOrderByteSize])
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s.SetBytes(signature[curveOrderByteSize:])
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return ecdsa.Verify(pubkey, digest[:], r, s)
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}
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