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// Package pkcs7 implements the subset of the CMS PKCS #7 datatype that is typically
// used to package certificates and CRLs. Using openssl, every certificate converted
// to PKCS #7 format from another encoding such as PEM conforms to this implementation.
// reference: https://www.openssl.org/docs/apps/crl2pkcs7.html
//
// PKCS #7 Data type, reference: https://tools.ietf.org/html/rfc2315
//
// The full pkcs#7 cryptographic message syntax allows for cryptographic enhancements,
// for example data can be encrypted and signed and then packaged through pkcs#7 to be
// sent over a network and then verified and decrypted. It is asn1, and the type of
// PKCS #7 ContentInfo, which comprises the PKCS #7 structure, is:
//
// ContentInfo ::= SEQUENCE {
// contentType ContentType,
// content [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL
// }
//
// There are 6 possible ContentTypes, data, signedData, envelopedData,
// signedAndEnvelopedData, digestedData, and encryptedData. Here signedData, Data, and encrypted
// Data are implemented, as the degenerate case of signedData without a signature is the typical
// format for transferring certificates and CRLS, and Data and encryptedData are used in PKCS #12
// formats.
// The ContentType signedData has the form:
//
//
// signedData ::= SEQUENCE {
// version Version,
// digestAlgorithms DigestAlgorithmIdentifiers,
// contentInfo ContentInfo,
// certificates [0] IMPLICIT ExtendedCertificatesAndCertificates OPTIONAL
// crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
// signerInfos SignerInfos
// }
//
// As of yet signerInfos and digestAlgorithms are not parsed, as they are not relevant to
// this system's use of PKCS #7 data. Version is an integer type, note that PKCS #7 is
// recursive, this second layer of ContentInfo is similar ignored for our degenerate
// usage. The ExtendedCertificatesAndCertificates type consists of a sequence of choices
// between PKCS #6 extended certificates and x509 certificates. Any sequence consisting
// of any number of extended certificates is not yet supported in this implementation.
//
// The ContentType Data is simply a raw octet string and is parsed directly into a Go []byte slice.
//
// The ContentType encryptedData is the most complicated and its form can be gathered by
// the go type below. It essentially contains a raw octet string of encrypted data and an
// algorithm identifier for use in decrypting this data.
package pkcs7
import (
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"errors"
cferr "github.com/cloudflare/cfssl/errors"
)
// Types used for asn1 Unmarshaling.
type signedData struct {
Version int
DigestAlgorithms asn1.RawValue
ContentInfo asn1.RawValue
Certificates asn1.RawValue `asn1:"optional" asn1:"tag:0"`
Crls asn1.RawValue `asn1:"optional"`
SignerInfos asn1.RawValue
}
type initPKCS7 struct {
Raw asn1.RawContent
ContentType asn1.ObjectIdentifier
Content asn1.RawValue `asn1:"tag:0,explicit,optional"`
}
// Object identifier strings of the three implemented PKCS7 types.
const (
ObjIDData = "1.2.840.113549.1.7.1"
ObjIDSignedData = "1.2.840.113549.1.7.2"
ObjIDEncryptedData = "1.2.840.113549.1.7.6"
)
// PKCS7 represents the ASN1 PKCS #7 Content type. It contains one of three
// possible types of Content objects, as denoted by the object identifier in
// the ContentInfo field, the other two being nil. SignedData
// is the degenerate SignedData Content info without signature used
// to hold certificates and crls. Data is raw bytes, and EncryptedData
// is as defined in PKCS #7 standard.
type PKCS7 struct {
Raw asn1.RawContent
ContentInfo string
Content Content
}
// Content implements three of the six possible PKCS7 data types. Only one is non-nil.
type Content struct {
Data []byte
SignedData SignedData
EncryptedData EncryptedData
}
// SignedData defines the typical carrier of certificates and crls.
type SignedData struct {
Raw asn1.RawContent
Version int
Certificates []*x509.Certificate
Crl *pkix.CertificateList
}
// Data contains raw bytes. Used as a subtype in PKCS12.
type Data struct {
Bytes []byte
}
// EncryptedData contains encrypted data. Used as a subtype in PKCS12.
type EncryptedData struct {
Raw asn1.RawContent
Version int
EncryptedContentInfo EncryptedContentInfo
}
// EncryptedContentInfo is a subtype of PKCS7EncryptedData.
type EncryptedContentInfo struct {
Raw asn1.RawContent
ContentType asn1.ObjectIdentifier
ContentEncryptionAlgorithm pkix.AlgorithmIdentifier
EncryptedContent []byte `asn1:"tag:0,optional"`
}
// ParsePKCS7 attempts to parse the DER encoded bytes of a
// PKCS7 structure.
func ParsePKCS7(raw []byte) (msg *PKCS7, err error) {
var pkcs7 initPKCS7
_, err = asn1.Unmarshal(raw, &pkcs7)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
msg = new(PKCS7)
msg.Raw = pkcs7.Raw
msg.ContentInfo = pkcs7.ContentType.String()
switch {
case msg.ContentInfo == ObjIDData:
msg.ContentInfo = "Data"
_, err = asn1.Unmarshal(pkcs7.Content.Bytes, &msg.Content.Data)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
case msg.ContentInfo == ObjIDSignedData:
msg.ContentInfo = "SignedData"
var signedData signedData
_, err = asn1.Unmarshal(pkcs7.Content.Bytes, &signedData)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
if len(signedData.Certificates.Bytes) != 0 {
msg.Content.SignedData.Certificates, err = x509.ParseCertificates(signedData.Certificates.Bytes)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
}
if len(signedData.Crls.Bytes) != 0 {
msg.Content.SignedData.Crl, err = x509.ParseDERCRL(signedData.Crls.Bytes)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
}
msg.Content.SignedData.Version = signedData.Version
msg.Content.SignedData.Raw = pkcs7.Content.Bytes
case msg.ContentInfo == ObjIDEncryptedData:
msg.ContentInfo = "EncryptedData"
var encryptedData EncryptedData
_, err = asn1.Unmarshal(pkcs7.Content.Bytes, &encryptedData)
if err != nil {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, err)
}
if encryptedData.Version != 0 {
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, errors.New("Only support for PKCS #7 encryptedData version 0"))
}
msg.Content.EncryptedData = encryptedData
default:
return nil, cferr.Wrap(cferr.CertificateError, cferr.ParseFailed, errors.New("Attempt to parse PKCS# 7 Content not of type data, signed data or encrypted data"))
}
return msg, nil
}
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