golang crypto X509KeyPair 简析

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// X509KeyPair parses a public/private key pair from a pair of
// PEM encoded data. On successful return, Certificate.Leaf will be nil because
// the parsed form of the certificate is not retained.
func X509KeyPair(certPEMBlock, keyPEMBlock []byte) (Certificate, error) {
...
}

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//tls.Certificate
// A Certificate is a chain of one or more certificates, leaf first.
type Certificate struct {
	Certificate [][]byte
	// PrivateKey contains the private key corresponding to the public key in
	// Leaf. This must implement crypto.Signer with an RSA, ECDSA or Ed25519 PublicKey.
	// For a server up to TLS 1.2, it can also implement crypto.Decrypter with
	// an RSA PublicKey.
	PrivateKey crypto.PrivateKey
	// SupportedSignatureAlgorithms is an optional list restricting what
	// signature algorithms the PrivateKey can be used for.
	SupportedSignatureAlgorithms []SignatureScheme
	// OCSPStaple contains an optional OCSP response which will be served
	// to clients that request it.
	OCSPStaple []byte
	// SignedCertificateTimestamps contains an optional list of Signed
	// Certificate Timestamps which will be served to clients that request it.
	SignedCertificateTimestamps [][]byte
	// Leaf is the parsed form of the leaf certificate, which may be initialized
	// using x509.ParseCertificate to reduce per-handshake processing. If nil,
	// the leaf certificate will be parsed as needed.
	Leaf *x509.Certificate
}

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//X509.certificate
// A Certificate represents an X.509 certificate.
type Certificate struct {
	Raw                     []byte // Complete ASN.1 DER content (certificate, signature algorithm and signature).
	RawTBSCertificate       []byte // Certificate part of raw ASN.1 DER content.
	RawSubjectPublicKeyInfo []byte // DER encoded SubjectPublicKeyInfo.
	RawSubject              []byte // DER encoded Subject
	RawIssuer               []byte // DER encoded Issuer

	Signature          []byte
	SignatureAlgorithm SignatureAlgorithm

	PublicKeyAlgorithm PublicKeyAlgorithm
	PublicKey          any

	Version             int
	SerialNumber        *big.Int
	Issuer              pkix.Name
	Subject             pkix.Name
	NotBefore, NotAfter time.Time // Validity bounds.
	KeyUsage            KeyUsage

	// Extensions contains raw X.509 extensions. When parsing certificates,
	// this can be used to extract non-critical extensions that are not
	// parsed by this package. When marshaling certificates, the Extensions
	// field is ignored, see ExtraExtensions.
	Extensions []pkix.Extension

	// ExtraExtensions contains extensions to be copied, raw, into any
	// marshaled certificates. Values override any extensions that would
	// otherwise be produced based on the other fields. The ExtraExtensions
	// field is not populated when parsing certificates, see Extensions.
	ExtraExtensions []pkix.Extension

	// UnhandledCriticalExtensions contains a list of extension IDs that
	// were not (fully) processed when parsing. Verify will fail if this
	// slice is non-empty, unless verification is delegated to an OS
	// library which understands all the critical extensions.
	//
	// Users can access these extensions using Extensions and can remove
	// elements from this slice if they believe that they have been
	// handled.
	UnhandledCriticalExtensions []asn1.ObjectIdentifier

	ExtKeyUsage        []ExtKeyUsage           // Sequence of extended key usages.
	UnknownExtKeyUsage []asn1.ObjectIdentifier // Encountered extended key usages unknown to this package.

	// BasicConstraintsValid indicates whether IsCA, MaxPathLen,
	// and MaxPathLenZero are valid.
	BasicConstraintsValid bool
	IsCA                  bool

	// MaxPathLen and MaxPathLenZero indicate the presence and
	// value of the BasicConstraints' "pathLenConstraint".
	//
	// When parsing a certificate, a positive non-zero MaxPathLen
	// means that the field was specified, -1 means it was unset,
	// and MaxPathLenZero being true mean that the field was
	// explicitly set to zero. The case of MaxPathLen==0 with MaxPathLenZero==false
	// should be treated equivalent to -1 (unset).
	//
	// When generating a certificate, an unset pathLenConstraint
	// can be requested with either MaxPathLen == -1 or using the
	// zero value for both MaxPathLen and MaxPathLenZero.
	MaxPathLen int
	// MaxPathLenZero indicates that BasicConstraintsValid==true
	// and MaxPathLen==0 should be interpreted as an actual
	// maximum path length of zero. Otherwise, that combination is
	// interpreted as MaxPathLen not being set.
	MaxPathLenZero bool

	SubjectKeyId   []byte
	AuthorityKeyId []byte

	// RFC 5280, 4.2.2.1 (Authority Information Access)
	OCSPServer            []string
	IssuingCertificateURL []string

	// Subject Alternate Name values. (Note that these values may not be valid
	// if invalid values were contained within a parsed certificate. For
	// example, an element of DNSNames may not be a valid DNS domain name.)
	DNSNames       []string
	EmailAddresses []string
	IPAddresses    []net.IP
	URIs           []*url.URL

	// Name constraints
	PermittedDNSDomainsCritical bool // if true then the name constraints are marked critical.
	PermittedDNSDomains         []string
	ExcludedDNSDomains          []string
	PermittedIPRanges           []*net.IPNet
	ExcludedIPRanges            []*net.IPNet
	PermittedEmailAddresses     []string
	ExcludedEmailAddresses      []string
	PermittedURIDomains         []string
	ExcludedURIDomains          []string

	// CRL Distribution Points
	CRLDistributionPoints []string

	PolicyIdentifiers []asn1.ObjectIdentifier
}

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func X509KeyPair(certPEMBlock, keyPEMBlock []byte) (Certificate, error) {
	fail := func(err error) (Certificate, error) { return Certificate{}, err }
//声明一个tls.Certificate
	var cert Certificate
	var skippedBlockTypes []string
    //对于证书（certPEMBlock）不断遍历将 type 为 CERTIFICATE 的 PEM 格式块加入到 cert.Certificate 中，将其他的 block 加入到 skippedBlockTypes 中
	for {
		var certDERBlock *pem.Block
		certDERBlock, certPEMBlock = pem.Decode(certPEMBlock)
		if certDERBlock == nil {
			break
		}
		if certDERBlock.Type == "CERTIFICATE" {
			cert.Certificate = append(cert.Certificate, certDERBlock.Bytes)
		} else {
			skippedBlockTypes = append(skippedBlockTypes, certDERBlock.Type)
		}
	}
//对上述处理结果进行处理，做一些错误分析
	if len(cert.Certificate) == 0 {
		if len(skippedBlockTypes) == 0 {
			return fail(errors.New("tls: failed to find any PEM data in certificate input"))
		}
		if len(skippedBlockTypes) == 1 && strings.HasSuffix(skippedBlockTypes[0], "PRIVATE KEY") {
			return fail(errors.New("tls: failed to find certificate PEM data in certificate input, but did find a private key; PEM inputs may have been switched"))
		}
		return fail(fmt.Errorf("tls: failed to find \"CERTIFICATE\" PEM block in certificate input after skipping PEM blocks of the following types: %v", skippedBlockTypes))
	}
//重置skippedBlockTypes
	skippedBlockTypes = skippedBlockTypes[:0]
	var keyDERBlock *pem.Block
    //遍历密钥(keyPEMBlock)，获取 type 为 PRIVATE KEY 的 PEM 格式块。
	for {
		keyDERBlock, keyPEMBlock = pem.Decode(keyPEMBlock)
        //对上述处理结果进行处理，做一些错误分析
		if keyDERBlock == nil {
			if len(skippedBlockTypes) == 0 {
				return fail(errors.New("tls: failed to find any PEM data in key input"))
			}
			if len(skippedBlockTypes) == 1 && skippedBlockTypes[0] == "CERTIFICATE" {
				return fail(errors.New("tls: found a certificate rather than a key in the PEM for the private key"))
			}
			return fail(fmt.Errorf("tls: failed to find PEM block with type ending in \"PRIVATE KEY\" in key input after skipping PEM blocks of the following types: %v", skippedBlockTypes))
		}
		if keyDERBlock.Type == "PRIVATE KEY" || strings.HasSuffix(keyDERBlock.Type, " PRIVATE KEY") {
			break
		}
		skippedBlockTypes = append(skippedBlockTypes, keyDERBlock.Type)
	}

	// We don't need to parse the public key for TLS, but we so do anyway
	// to check that it looks sane and matches the private key.
    //将[]byte类型的Certificate转换为x509.Certificate
	x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
	if err != nil {
		return fail(err)
	}
//将[]byte型的keyDERBlock转换后加入到cert.PrivateKey中
	cert.PrivateKey, err = parsePrivateKey(keyDERBlock.Bytes)
	if err != nil {
		return fail(err)
	}
//检查获取的Certificate中的publicKey是否与PrivateKey匹配
	switch pub := x509Cert.PublicKey.(type) {
	case *rsa.PublicKey:
		priv, ok := cert.PrivateKey.(*rsa.PrivateKey)
		if !ok {
			return fail(errors.New("tls: private key type does not match public key type"))
		}
		if pub.N.Cmp(priv.N) != 0 {
			return fail(errors.New("tls: private key does not match public key"))
		}
	case *ecdsa.PublicKey:
		priv, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
		if !ok {
			return fail(errors.New("tls: private key type does not match public key type"))
		}
		if pub.X.Cmp(priv.X) != 0 || pub.Y.Cmp(priv.Y) != 0 {
			return fail(errors.New("tls: private key does not match public key"))
		}
	case ed25519.PublicKey:
		priv, ok := cert.PrivateKey.(ed25519.PrivateKey)
		if !ok {
			return fail(errors.New("tls: private key type does not match public key type"))
		}
		if !bytes.Equal(priv.Public().(ed25519.PublicKey), pub) {
			return fail(errors.New("tls: private key does not match public key"))
		}
	default:
		return fail(errors.New("tls: unknown public key algorithm"))
	}

	return cert, nil
}