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GopherCon 2019 Review: PKI for Gophers Hunter Chen

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● Original Presenter: Eric Chiang ● Original Slides: ○ Code Samples ○ Brief explanation of security concepts ● Liveblog of the Presentation: ● Video will be posted in the future (along with all the other talks at GopherCon 2019): Original Presentation

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● ECDSA Package: func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error) func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool type PrivateKey func GenerateKey(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) func (priv *PrivateKey) Public() crypto.PublicKey func (priv *PrivateKey) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) type PublicKey ● Elliptic Package ● SHA512 Package ● Generate Key → Hash → Sign → Verify ● Note: When generating, use crypto/rand, not math/rand Digital Signatures

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● X509 Package: func CreateCertificate(rand io.Reader, template, parent *Certificate, pub, priv interface{}) (cert []byte, err error) func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) type Certificate func ParseCertificate(asn1Data []byte) (*Certificate, error) func (c *Certificate) CheckSignature(algo SignatureAlgorithm, signed, signature []byte) error func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) … ● Generate Key → Create Cert Template → Create Cert → Marshal Key → Encode Key and Cert ● Go marshals the key into DER format ● PEM Package Certificates

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● Serving Certificates: ○ Generate certificate ○ Use TLS Package to load certificate and private key as TLS certificate ○ Pass TLS certificate into TLSConfig when creating server ○ Configure Client to trust server ■ add certificate into pool ● Client Certificates: ○ Same process ■ Generate certificate ■ Create TLS certificate ■ Pass TLS certificate into client config when creating client ■ Configure server to authenticate clients ● Also add client CA into pool Serving Certificates and Client Certificates

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● Making Requests ○ X509 Package func CreateCertificateRequest(rand io.Reader, template *CertificateRequest, priv interface{}) (csr []byte, err error) type CertificateRequest func ParseCertificateRequest(asn1Data []byte) (*CertificateRequest, error) func (c *CertificateRequest) CheckSignature() error ○ Generate Key → Create Request → Send Request ○ Parse Request → Check Signature → Create Certificate → Send Certificate ● Authentication (With JWTs) ○ Get JWT from header of request → Parse → Verify with CA ■ Many different packages and ways to verify JWT. Pick your favorite Certificate Signing Requests (CSRs)

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● Not that good ○ Fails open ○ Better for smaller number of certifications ● Use OCSP instead ○ In the TLS Package ■ Certificate struct has a OCSPStaple []byte field ○ Create OCSPResponse using OCSP Package under /x/crypto func CreateResponse(issuer, responderCert *x509.Certificate, template Response, priv crypto.Signer) ([]byte, error) type Response func ParseResponse(bytes []byte, issuer *x509.Certificate) (*Response, error) func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Response, error) ○ Create Response → Send Response ○ For reading OCSP ■ Loop through certificate chain → Parse each OCSP Response Certificate Revocation Lists (CRLs) and OCSPs

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● Just set the GetCertificate field in the TLS config ○ Pass a function with a switch statement for each domain ○ Return the corresponding certificate for each domain ● Go does not support encrypted SNIs Server Name Identification (SNIs)

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● Golang supports hardware keys ○ tls.Certificate has a field called PrivateKey ○ Use manufacturer libraries to pass the interface into the CreateCertificateRequest method ■ Example: YubiKey ● ● yk.GenerateECWithPolicies ● Pass into x509.CreateCertificateRequest ● Or, pass into field PrivateKey when creating tls.Certificate Hardware Keys

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● Logs every certificate signed by an authority ● Make a request to CT endpoint ○ ● Use CT Client to make request ○ Client Package type LogClient func New(uri string, hc *http.Client, opts jsonclient.Options) (*LogClient, error) func (c *LogClient) GetEntries(ctx context.Context, start, end int64) ([]ct.LogEntry, error) func (c *LogClient) GetSTH(ctx context.Context) (*ct.SignedTreeHead, error) ○ Make new Client → Get STH → Get Entries Certificate Transparency

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Thank you! Finished!