diff options
Diffstat (limited to 'vendor/github.com/fullsailor/pkcs7/pkcs7.go')
| -rw-r--r-- | vendor/github.com/fullsailor/pkcs7/pkcs7.go | 962 |
1 files changed, 962 insertions, 0 deletions
diff --git a/vendor/github.com/fullsailor/pkcs7/pkcs7.go b/vendor/github.com/fullsailor/pkcs7/pkcs7.go new file mode 100644 index 000000000..0264466b4 --- /dev/null +++ b/vendor/github.com/fullsailor/pkcs7/pkcs7.go @@ -0,0 +1,962 @@ +// Package pkcs7 implements parsing and generation of some PKCS#7 structures. +package pkcs7 + +import ( + "bytes" + "crypto" + "crypto/aes" + "crypto/cipher" + "crypto/des" + "crypto/hmac" + "crypto/rand" + "crypto/rsa" + "crypto/x509" + "crypto/x509/pkix" + "encoding/asn1" + "errors" + "fmt" + "math/big" + "sort" + "time" + + _ "crypto/sha1" // for crypto.SHA1 +) + +// PKCS7 Represents a PKCS7 structure +type PKCS7 struct { + Content []byte + Certificates []*x509.Certificate + CRLs []pkix.CertificateList + Signers []signerInfo + raw interface{} +} + +type contentInfo struct { + ContentType asn1.ObjectIdentifier + Content asn1.RawValue `asn1:"explicit,optional,tag:0"` +} + +// ErrUnsupportedContentType is returned when a PKCS7 content is not supported. +// Currently only Data (1.2.840.113549.1.7.1), Signed Data (1.2.840.113549.1.7.2), +// and Enveloped Data are supported (1.2.840.113549.1.7.3) +var ErrUnsupportedContentType = errors.New("pkcs7: cannot parse data: unimplemented content type") + +type unsignedData []byte + +var ( + oidData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 1} + oidSignedData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 2} + oidEnvelopedData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 3} + oidSignedAndEnvelopedData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 4} + oidDigestedData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 5} + oidEncryptedData = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 7, 6} + oidAttributeContentType = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 3} + oidAttributeMessageDigest = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 4} + oidAttributeSigningTime = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 5} +) + +type signedData struct { + Version int `asn1:"default:1"` + DigestAlgorithmIdentifiers []pkix.AlgorithmIdentifier `asn1:"set"` + ContentInfo contentInfo + Certificates rawCertificates `asn1:"optional,tag:0"` + CRLs []pkix.CertificateList `asn1:"optional,tag:1"` + SignerInfos []signerInfo `asn1:"set"` +} + +type rawCertificates struct { + Raw asn1.RawContent +} + +type envelopedData struct { + Version int + RecipientInfos []recipientInfo `asn1:"set"` + EncryptedContentInfo encryptedContentInfo +} + +type recipientInfo struct { + Version int + IssuerAndSerialNumber issuerAndSerial + KeyEncryptionAlgorithm pkix.AlgorithmIdentifier + EncryptedKey []byte +} + +type encryptedContentInfo struct { + ContentType asn1.ObjectIdentifier + ContentEncryptionAlgorithm pkix.AlgorithmIdentifier + EncryptedContent asn1.RawValue `asn1:"tag:0,optional"` +} + +type attribute struct { + Type asn1.ObjectIdentifier + Value asn1.RawValue `asn1:"set"` +} + +type issuerAndSerial struct { + IssuerName asn1.RawValue + SerialNumber *big.Int +} + +// MessageDigestMismatchError is returned when the signer data digest does not +// match the computed digest for the contained content +type MessageDigestMismatchError struct { + ExpectedDigest []byte + ActualDigest []byte +} + +func (err *MessageDigestMismatchError) Error() string { + return fmt.Sprintf("pkcs7: Message digest mismatch\n\tExpected: %X\n\tActual : %X", err.ExpectedDigest, err.ActualDigest) +} + +type signerInfo struct { + Version int `asn1:"default:1"` + IssuerAndSerialNumber issuerAndSerial + DigestAlgorithm pkix.AlgorithmIdentifier + AuthenticatedAttributes []attribute `asn1:"optional,tag:0"` + DigestEncryptionAlgorithm pkix.AlgorithmIdentifier + EncryptedDigest []byte + UnauthenticatedAttributes []attribute `asn1:"optional,tag:1"` +} + +// Parse decodes a DER encoded PKCS7 package +func Parse(data []byte) (p7 *PKCS7, err error) { + if len(data) == 0 { + return nil, errors.New("pkcs7: input data is empty") + } + var info contentInfo + der, err := ber2der(data) + if err != nil { + return nil, err + } + rest, err := asn1.Unmarshal(der, &info) + if len(rest) > 0 { + err = asn1.SyntaxError{Msg: "trailing data"} + return + } + if err != nil { + return + } + + // fmt.Printf("--> Content Type: %s", info.ContentType) + switch { + case info.ContentType.Equal(oidSignedData): + return parseSignedData(info.Content.Bytes) + case info.ContentType.Equal(oidEnvelopedData): + return parseEnvelopedData(info.Content.Bytes) + } + return nil, ErrUnsupportedContentType +} + +func parseSignedData(data []byte) (*PKCS7, error) { + var sd signedData + asn1.Unmarshal(data, &sd) + certs, err := sd.Certificates.Parse() + if err != nil { + return nil, err + } + // fmt.Printf("--> Signed Data Version %d\n", sd.Version) + + var compound asn1.RawValue + var content unsignedData + + // The Content.Bytes maybe empty on PKI responses. + if len(sd.ContentInfo.Content.Bytes) > 0 { + if _, err := asn1.Unmarshal(sd.ContentInfo.Content.Bytes, &compound); err != nil { + return nil, err + } + } + // Compound octet string + if compound.IsCompound { + if _, err = asn1.Unmarshal(compound.Bytes, &content); err != nil { + return nil, err + } + } else { + // assuming this is tag 04 + content = compound.Bytes + } + return &PKCS7{ + Content: content, + Certificates: certs, + CRLs: sd.CRLs, + Signers: sd.SignerInfos, + raw: sd}, nil +} + +func (raw rawCertificates) Parse() ([]*x509.Certificate, error) { + if len(raw.Raw) == 0 { + return nil, nil + } + + var val asn1.RawValue + if _, err := asn1.Unmarshal(raw.Raw, &val); err != nil { + return nil, err + } + + return x509.ParseCertificates(val.Bytes) +} + +func parseEnvelopedData(data []byte) (*PKCS7, error) { + var ed envelopedData + if _, err := asn1.Unmarshal(data, &ed); err != nil { + return nil, err + } + return &PKCS7{ + raw: ed, + }, nil +} + +// Verify checks the signatures of a PKCS7 object +// WARNING: Verify does not check signing time or verify certificate chains at +// this time. +func (p7 *PKCS7) Verify() (err error) { + if len(p7.Signers) == 0 { + return errors.New("pkcs7: Message has no signers") + } + for _, signer := range p7.Signers { + if err := verifySignature(p7, signer); err != nil { + return err + } + } + return nil +} + +func verifySignature(p7 *PKCS7, signer signerInfo) error { + signedData := p7.Content + hash, err := getHashForOID(signer.DigestAlgorithm.Algorithm) + if err != nil { + return err + } + if len(signer.AuthenticatedAttributes) > 0 { + // TODO(fullsailor): First check the content type match + var digest []byte + err := unmarshalAttribute(signer.AuthenticatedAttributes, oidAttributeMessageDigest, &digest) + if err != nil { + return err + } + h := hash.New() + h.Write(p7.Content) + computed := h.Sum(nil) + if !hmac.Equal(digest, computed) { + return &MessageDigestMismatchError{ + ExpectedDigest: digest, + ActualDigest: computed, + } + } + // TODO(fullsailor): Optionally verify certificate chain + // TODO(fullsailor): Optionally verify signingTime against certificate NotAfter/NotBefore + signedData, err = marshalAttributes(signer.AuthenticatedAttributes) + if err != nil { + return err + } + } + cert := getCertFromCertsByIssuerAndSerial(p7.Certificates, signer.IssuerAndSerialNumber) + if cert == nil { + return errors.New("pkcs7: No certificate for signer") + } + + algo := getSignatureAlgorithmFromAI(signer.DigestEncryptionAlgorithm) + if algo == x509.UnknownSignatureAlgorithm { + // I'm not sure what the spec here is, and the openssl sources were not + // helpful. But, this is what App Store receipts appear to do. + // The DigestEncryptionAlgorithm is just "rsaEncryption (PKCS #1)" + // But we're expecting a digest + encryption algorithm. So... we're going + // to determine an algorithm based on the DigestAlgorithm and this + // encryption algorithm. + if signer.DigestEncryptionAlgorithm.Algorithm.Equal(oidEncryptionAlgorithmRSA) { + algo = getRSASignatureAlgorithmForDigestAlgorithm(hash) + } + } + return cert.CheckSignature(algo, signedData, signer.EncryptedDigest) +} + +func marshalAttributes(attrs []attribute) ([]byte, error) { + encodedAttributes, err := asn1.Marshal(struct { + A []attribute `asn1:"set"` + }{A: attrs}) + if err != nil { + return nil, err + } + + // Remove the leading sequence octets + var raw asn1.RawValue + asn1.Unmarshal(encodedAttributes, &raw) + return raw.Bytes, nil +} + +var ( + oidDigestAlgorithmSHA1 = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 26} + oidEncryptionAlgorithmRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1} +) + +func getCertFromCertsByIssuerAndSerial(certs []*x509.Certificate, ias issuerAndSerial) *x509.Certificate { + for _, cert := range certs { + if isCertMatchForIssuerAndSerial(cert, ias) { + return cert + } + } + return nil +} + +func getHashForOID(oid asn1.ObjectIdentifier) (crypto.Hash, error) { + switch { + case oid.Equal(oidDigestAlgorithmSHA1): + return crypto.SHA1, nil + case oid.Equal(oidSHA256): + return crypto.SHA256, nil + } + return crypto.Hash(0), ErrUnsupportedAlgorithm +} + +func getRSASignatureAlgorithmForDigestAlgorithm(hash crypto.Hash) x509.SignatureAlgorithm { + for _, details := range signatureAlgorithmDetails { + if details.pubKeyAlgo == x509.RSA && details.hash == hash { + return details.algo + } + } + return x509.UnknownSignatureAlgorithm +} + +// GetOnlySigner returns an x509.Certificate for the first signer of the signed +// data payload. If there are more or less than one signer, nil is returned +func (p7 *PKCS7) GetOnlySigner() *x509.Certificate { + if len(p7.Signers) != 1 { + return nil + } + signer := p7.Signers[0] + return getCertFromCertsByIssuerAndSerial(p7.Certificates, signer.IssuerAndSerialNumber) +} + +// ErrUnsupportedAlgorithm tells you when our quick dev assumptions have failed +var ErrUnsupportedAlgorithm = errors.New("pkcs7: cannot decrypt data: only RSA, DES, DES-EDE3, AES-256-CBC and AES-128-GCM supported") + +// ErrNotEncryptedContent is returned when attempting to Decrypt data that is not encrypted data +var ErrNotEncryptedContent = errors.New("pkcs7: content data is a decryptable data type") + +// Decrypt decrypts encrypted content info for recipient cert and private key +func (p7 *PKCS7) Decrypt(cert *x509.Certificate, pk crypto.PrivateKey) ([]byte, error) { + data, ok := p7.raw.(envelopedData) + if !ok { + return nil, ErrNotEncryptedContent + } + recipient := selectRecipientForCertificate(data.RecipientInfos, cert) + if recipient.EncryptedKey == nil { + return nil, errors.New("pkcs7: no enveloped recipient for provided certificate") + } + if priv := pk.(*rsa.PrivateKey); priv != nil { + var contentKey []byte + contentKey, err := rsa.DecryptPKCS1v15(rand.Reader, priv, recipient.EncryptedKey) + if err != nil { + return nil, err + } + return data.EncryptedContentInfo.decrypt(contentKey) + } + fmt.Printf("Unsupported Private Key: %v\n", pk) + return nil, ErrUnsupportedAlgorithm +} + +var oidEncryptionAlgorithmDESCBC = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 7} +var oidEncryptionAlgorithmDESEDE3CBC = asn1.ObjectIdentifier{1, 2, 840, 113549, 3, 7} +var oidEncryptionAlgorithmAES256CBC = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 1, 42} +var oidEncryptionAlgorithmAES128GCM = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 1, 6} +var oidEncryptionAlgorithmAES128CBC = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 1, 2} + +func (eci encryptedContentInfo) decrypt(key []byte) ([]byte, error) { + alg := eci.ContentEncryptionAlgorithm.Algorithm + if !alg.Equal(oidEncryptionAlgorithmDESCBC) && + !alg.Equal(oidEncryptionAlgorithmDESEDE3CBC) && + !alg.Equal(oidEncryptionAlgorithmAES256CBC) && + !alg.Equal(oidEncryptionAlgorithmAES128CBC) && + !alg.Equal(oidEncryptionAlgorithmAES128GCM) { + fmt.Printf("Unsupported Content Encryption Algorithm: %s\n", alg) + return nil, ErrUnsupportedAlgorithm + } + + // EncryptedContent can either be constructed of multple OCTET STRINGs + // or _be_ a tagged OCTET STRING + var cyphertext []byte + if eci.EncryptedContent.IsCompound { + // Complex case to concat all of the children OCTET STRINGs + var buf bytes.Buffer + cypherbytes := eci.EncryptedContent.Bytes + for { + var part []byte + cypherbytes, _ = asn1.Unmarshal(cypherbytes, &part) + buf.Write(part) + if cypherbytes == nil { + break + } + } + cyphertext = buf.Bytes() + } else { + // Simple case, the bytes _are_ the cyphertext + cyphertext = eci.EncryptedContent.Bytes + } + + var block cipher.Block + var err error + + switch { + case alg.Equal(oidEncryptionAlgorithmDESCBC): + block, err = des.NewCipher(key) + case alg.Equal(oidEncryptionAlgorithmDESEDE3CBC): + block, err = des.NewTripleDESCipher(key) + case alg.Equal(oidEncryptionAlgorithmAES256CBC): + fallthrough + case alg.Equal(oidEncryptionAlgorithmAES128GCM), alg.Equal(oidEncryptionAlgorithmAES128CBC): + block, err = aes.NewCipher(key) + } + + if err != nil { + return nil, err + } + + if alg.Equal(oidEncryptionAlgorithmAES128GCM) { + params := aesGCMParameters{} + paramBytes := eci.ContentEncryptionAlgorithm.Parameters.Bytes + + _, err := asn1.Unmarshal(paramBytes, ¶ms) + if err != nil { + return nil, err + } + + gcm, err := cipher.NewGCM(block) + if err != nil { + return nil, err + } + + if len(params.Nonce) != gcm.NonceSize() { + return nil, errors.New("pkcs7: encryption algorithm parameters are incorrect") + } + if params.ICVLen != gcm.Overhead() { + return nil, errors.New("pkcs7: encryption algorithm parameters are incorrect") + } + + plaintext, err := gcm.Open(nil, params.Nonce, cyphertext, nil) + if err != nil { + return nil, err + } + + return plaintext, nil + } + + iv := eci.ContentEncryptionAlgorithm.Parameters.Bytes + if len(iv) != block.BlockSize() { + return nil, errors.New("pkcs7: encryption algorithm parameters are malformed") + } + mode := cipher.NewCBCDecrypter(block, iv) + plaintext := make([]byte, len(cyphertext)) + mode.CryptBlocks(plaintext, cyphertext) + if plaintext, err = unpad(plaintext, mode.BlockSize()); err != nil { + return nil, err + } + return plaintext, nil +} + +func selectRecipientForCertificate(recipients []recipientInfo, cert *x509.Certificate) recipientInfo { + for _, recp := range recipients { + if isCertMatchForIssuerAndSerial(cert, recp.IssuerAndSerialNumber) { + return recp + } + } + return recipientInfo{} +} + +func isCertMatchForIssuerAndSerial(cert *x509.Certificate, ias issuerAndSerial) bool { + return cert.SerialNumber.Cmp(ias.SerialNumber) == 0 && bytes.Compare(cert.RawIssuer, ias.IssuerName.FullBytes) == 0 +} + +func pad(data []byte, blocklen int) ([]byte, error) { + if blocklen < 1 { + return nil, fmt.Errorf("invalid blocklen %d", blocklen) + } + padlen := blocklen - (len(data) % blocklen) + if padlen == 0 { + padlen = blocklen + } + pad := bytes.Repeat([]byte{byte(padlen)}, padlen) + return append(data, pad...), nil +} + +func unpad(data []byte, blocklen int) ([]byte, error) { + if blocklen < 1 { + return nil, fmt.Errorf("invalid blocklen %d", blocklen) + } + if len(data)%blocklen != 0 || len(data) == 0 { + return nil, fmt.Errorf("invalid data len %d", len(data)) + } + + // the last byte is the length of padding + padlen := int(data[len(data)-1]) + + // check padding integrity, all bytes should be the same + pad := data[len(data)-padlen:] + for _, padbyte := range pad { + if padbyte != byte(padlen) { + return nil, errors.New("invalid padding") + } + } + + return data[:len(data)-padlen], nil +} + +func unmarshalAttribute(attrs []attribute, attributeType asn1.ObjectIdentifier, out interface{}) error { + for _, attr := range attrs { + if attr.Type.Equal(attributeType) { + _, err := asn1.Unmarshal(attr.Value.Bytes, out) + return err + } + } + return errors.New("pkcs7: attribute type not in attributes") +} + +// UnmarshalSignedAttribute decodes a single attribute from the signer info +func (p7 *PKCS7) UnmarshalSignedAttribute(attributeType asn1.ObjectIdentifier, out interface{}) error { + sd, ok := p7.raw.(signedData) + if !ok { + return errors.New("pkcs7: payload is not signedData content") + } + if len(sd.SignerInfos) < 1 { + return errors.New("pkcs7: payload has no signers") + } + attributes := sd.SignerInfos[0].AuthenticatedAttributes + return unmarshalAttribute(attributes, attributeType, out) +} + +// SignedData is an opaque data structure for creating signed data payloads +type SignedData struct { + sd signedData + certs []*x509.Certificate + messageDigest []byte +} + +// Attribute represents a key value pair attribute. Value must be marshalable byte +// `encoding/asn1` +type Attribute struct { + Type asn1.ObjectIdentifier + Value interface{} +} + +// SignerInfoConfig are optional values to include when adding a signer +type SignerInfoConfig struct { + ExtraSignedAttributes []Attribute +} + +// NewSignedData initializes a SignedData with content +func NewSignedData(data []byte) (*SignedData, error) { + content, err := asn1.Marshal(data) + if err != nil { + return nil, err + } + ci := contentInfo{ + ContentType: oidData, + Content: asn1.RawValue{Class: 2, Tag: 0, Bytes: content, IsCompound: true}, + } + digAlg := pkix.AlgorithmIdentifier{ + Algorithm: oidDigestAlgorithmSHA1, + } + h := crypto.SHA1.New() + h.Write(data) + md := h.Sum(nil) + sd := signedData{ + ContentInfo: ci, + Version: 1, + DigestAlgorithmIdentifiers: []pkix.AlgorithmIdentifier{digAlg}, + } + return &SignedData{sd: sd, messageDigest: md}, nil +} + +type attributes struct { + types []asn1.ObjectIdentifier + values []interface{} +} + +// Add adds the attribute, maintaining insertion order +func (attrs *attributes) Add(attrType asn1.ObjectIdentifier, value interface{}) { + attrs.types = append(attrs.types, attrType) + attrs.values = append(attrs.values, value) +} + +type sortableAttribute struct { + SortKey []byte + Attribute attribute +} + +type attributeSet []sortableAttribute + +func (sa attributeSet) Len() int { + return len(sa) +} + +func (sa attributeSet) Less(i, j int) bool { + return bytes.Compare(sa[i].SortKey, sa[j].SortKey) < 0 +} + +func (sa attributeSet) Swap(i, j int) { + sa[i], sa[j] = sa[j], sa[i] +} + +func (sa attributeSet) Attributes() []attribute { + attrs := make([]attribute, len(sa)) + for i, attr := range sa { + attrs[i] = attr.Attribute + } + return attrs +} + +func (attrs *attributes) ForMarshaling() ([]attribute, error) { + sortables := make(attributeSet, len(attrs.types)) + for i := range sortables { + attrType := attrs.types[i] + attrValue := attrs.values[i] + asn1Value, err := asn1.Marshal(attrValue) + if err != nil { + return nil, err + } + attr := attribute{ + Type: attrType, + Value: asn1.RawValue{Tag: 17, IsCompound: true, Bytes: asn1Value}, // 17 == SET tag + } + encoded, err := asn1.Marshal(attr) + if err != nil { + return nil, err + } + sortables[i] = sortableAttribute{ + SortKey: encoded, + Attribute: attr, + } + } + sort.Sort(sortables) + return sortables.Attributes(), nil +} + +// AddSigner signs attributes about the content and adds certificate to payload +func (sd *SignedData) AddSigner(cert *x509.Certificate, pkey crypto.PrivateKey, config SignerInfoConfig) error { + attrs := &attributes{} + attrs.Add(oidAttributeContentType, sd.sd.ContentInfo.ContentType) + attrs.Add(oidAttributeMessageDigest, sd.messageDigest) + attrs.Add(oidAttributeSigningTime, time.Now()) + for _, attr := range config.ExtraSignedAttributes { + attrs.Add(attr.Type, attr.Value) + } + finalAttrs, err := attrs.ForMarshaling() + if err != nil { + return err + } + signature, err := signAttributes(finalAttrs, pkey, crypto.SHA1) + if err != nil { + return err + } + + ias, err := cert2issuerAndSerial(cert) + if err != nil { + return err + } + + signer := signerInfo{ + AuthenticatedAttributes: finalAttrs, + DigestAlgorithm: pkix.AlgorithmIdentifier{Algorithm: oidDigestAlgorithmSHA1}, + DigestEncryptionAlgorithm: pkix.AlgorithmIdentifier{Algorithm: oidSignatureSHA1WithRSA}, + IssuerAndSerialNumber: ias, + EncryptedDigest: signature, + Version: 1, + } + // create signature of signed attributes + sd.certs = append(sd.certs, cert) + sd.sd.SignerInfos = append(sd.sd.SignerInfos, signer) + return nil +} + +// AddCertificate adds the certificate to the payload. Useful for parent certificates +func (sd *SignedData) AddCertificate(cert *x509.Certificate) { + sd.certs = append(sd.certs, cert) +} + +// Detach removes content from the signed data struct to make it a detached signature. +// This must be called right before Finish() +func (sd *SignedData) Detach() { + sd.sd.ContentInfo = contentInfo{ContentType: oidData} +} + +// Finish marshals the content and its signers +func (sd *SignedData) Finish() ([]byte, error) { + sd.sd.Certificates = marshalCertificates(sd.certs) + inner, err := asn1.Marshal(sd.sd) + if err != nil { + return nil, err + } + outer := contentInfo{ + ContentType: oidSignedData, + Content: asn1.RawValue{Class: 2, Tag: 0, Bytes: inner, IsCompound: true}, + } + return asn1.Marshal(outer) +} + +func cert2issuerAndSerial(cert *x509.Certificate) (issuerAndSerial, error) { + var ias issuerAndSerial + // The issuer RDNSequence has to match exactly the sequence in the certificate + // We cannot use cert.Issuer.ToRDNSequence() here since it mangles the sequence + ias.IssuerName = asn1.RawValue{FullBytes: cert.RawIssuer} + ias.SerialNumber = cert.SerialNumber + + return ias, nil +} + +// signs the DER encoded form of the attributes with the private key +func signAttributes(attrs []attribute, pkey crypto.PrivateKey, hash crypto.Hash) ([]byte, error) { + attrBytes, err := marshalAttributes(attrs) + if err != nil { + return nil, err + } + h := hash.New() + h.Write(attrBytes) + hashed := h.Sum(nil) + switch priv := pkey.(type) { + case *rsa.PrivateKey: + return rsa.SignPKCS1v15(rand.Reader, priv, crypto.SHA1, hashed) + } + return nil, ErrUnsupportedAlgorithm +} + +// concats and wraps the certificates in the RawValue structure +func marshalCertificates(certs []*x509.Certificate) rawCertificates { + var buf bytes.Buffer + for _, cert := range certs { + buf.Write(cert.Raw) + } + rawCerts, _ := marshalCertificateBytes(buf.Bytes()) + return rawCerts +} + +// Even though, the tag & length are stripped out during marshalling the +// RawContent, we have to encode it into the RawContent. If its missing, +// then `asn1.Marshal()` will strip out the certificate wrapper instead. +func marshalCertificateBytes(certs []byte) (rawCertificates, error) { + var val = asn1.RawValue{Bytes: certs, Class: 2, Tag: 0, IsCompound: true} + b, err := asn1.Marshal(val) + if err != nil { + return rawCertificates{}, err + } + return rawCertificates{Raw: b}, nil +} + +// DegenerateCertificate creates a signed data structure containing only the +// provided certificate or certificate chain. +func DegenerateCertificate(cert []byte) ([]byte, error) { + rawCert, err := marshalCertificateBytes(cert) + if err != nil { + return nil, err + } + emptyContent := contentInfo{ContentType: oidData} + sd := signedData{ + Version: 1, + ContentInfo: emptyContent, + Certificates: rawCert, + CRLs: []pkix.CertificateList{}, + } + content, err := asn1.Marshal(sd) + if err != nil { + return nil, err + } + signedContent := contentInfo{ + ContentType: oidSignedData, + Content: asn1.RawValue{Class: 2, Tag: 0, Bytes: content, IsCompound: true}, + } + return asn1.Marshal(signedContent) +} + +const ( + EncryptionAlgorithmDESCBC = iota + EncryptionAlgorithmAES128GCM +) + +// ContentEncryptionAlgorithm determines the algorithm used to encrypt the +// plaintext message. Change the value of this variable to change which +// algorithm is used in the Encrypt() function. +var ContentEncryptionAlgorithm = EncryptionAlgorithmDESCBC + +// ErrUnsupportedEncryptionAlgorithm is returned when attempting to encrypt +// content with an unsupported algorithm. +var ErrUnsupportedEncryptionAlgorithm = errors.New("pkcs7: cannot encrypt content: only DES-CBC and AES-128-GCM supported") + +const nonceSize = 12 + +type aesGCMParameters struct { + Nonce []byte `asn1:"tag:4"` + ICVLen int +} + +func encryptAES128GCM(content []byte) ([]byte, *encryptedContentInfo, error) { + // Create AES key and nonce + key := make([]byte, 16) + nonce := make([]byte, nonceSize) + + _, err := rand.Read(key) + if err != nil { + return nil, nil, err + } + + _, err = rand.Read(nonce) + if err != nil { + return nil, nil, err + } + + // Encrypt content + block, err := aes.NewCipher(key) + if err != nil { + return nil, nil, err + } + + gcm, err := cipher.NewGCM(block) + if err != nil { + return nil, nil, err + } + + ciphertext := gcm.Seal(nil, nonce, content, nil) + + // Prepare ASN.1 Encrypted Content Info + paramSeq := aesGCMParameters{ + Nonce: nonce, + ICVLen: gcm.Overhead(), + } + + paramBytes, err := asn1.Marshal(paramSeq) + if err != nil { + return nil, nil, err + } + + eci := encryptedContentInfo{ + ContentType: oidData, + ContentEncryptionAlgorithm: pkix.AlgorithmIdentifier{ + Algorithm: oidEncryptionAlgorithmAES128GCM, + Parameters: asn1.RawValue{ + Tag: asn1.TagSequence, + Bytes: paramBytes, + }, + }, + EncryptedContent: marshalEncryptedContent(ciphertext), + } + + return key, &eci, nil +} + +func encryptDESCBC(content []byte) ([]byte, *encryptedContentInfo, error) { + // Create DES key & CBC IV + key := make([]byte, 8) + iv := make([]byte, des.BlockSize) + _, err := rand.Read(key) + if err != nil { + return nil, nil, err + } + _, err = rand.Read(iv) + if err != nil { + return nil, nil, err + } + + // Encrypt padded content + block, err := des.NewCipher(key) + if err != nil { + return nil, nil, err + } + mode := cipher.NewCBCEncrypter(block, iv) + plaintext, err := pad(content, mode.BlockSize()) + cyphertext := make([]byte, len(plaintext)) + mode.CryptBlocks(cyphertext, plaintext) + + // Prepare ASN.1 Encrypted Content Info + eci := encryptedContentInfo{ + ContentType: oidData, + ContentEncryptionAlgorithm: pkix.AlgorithmIdentifier{ + Algorithm: oidEncryptionAlgorithmDESCBC, + Parameters: asn1.RawValue{Tag: 4, Bytes: iv}, + }, + EncryptedContent: marshalEncryptedContent(cyphertext), + } + + return key, &eci, nil +} + +// Encrypt creates and returns an envelope data PKCS7 structure with encrypted +// recipient keys for each recipient public key. +// +// The algorithm used to perform encryption is determined by the current value +// of the global ContentEncryptionAlgorithm package variable. By default, the +// value is EncryptionAlgorithmDESCBC. To use a different algorithm, change the +// value before calling Encrypt(). For example: +// +// ContentEncryptionAlgorithm = EncryptionAlgorithmAES128GCM +// +// TODO(fullsailor): Add support for encrypting content with other algorithms +func Encrypt(content []byte, recipients []*x509.Certificate) ([]byte, error) { + var eci *encryptedContentInfo + var key []byte + var err error + + // Apply chosen symmetric encryption method + switch ContentEncryptionAlgorithm { + case EncryptionAlgorithmDESCBC: + key, eci, err = encryptDESCBC(content) + + case EncryptionAlgorithmAES128GCM: + key, eci, err = encryptAES128GCM(content) + + default: + return nil, ErrUnsupportedEncryptionAlgorithm + } + + if err != nil { + return nil, err + } + + // Prepare each recipient's encrypted cipher key + recipientInfos := make([]recipientInfo, len(recipients)) + for i, recipient := range recipients { + encrypted, err := encryptKey(key, recipient) + if err != nil { + return nil, err + } + ias, err := cert2issuerAndSerial(recipient) + if err != nil { + return nil, err + } + info := recipientInfo{ + Version: 0, + IssuerAndSerialNumber: ias, + KeyEncryptionAlgorithm: pkix.AlgorithmIdentifier{ + Algorithm: oidEncryptionAlgorithmRSA, + }, + EncryptedKey: encrypted, + } + recipientInfos[i] = info + } + + // Prepare envelope content + envelope := envelopedData{ + EncryptedContentInfo: *eci, + Version: 0, + RecipientInfos: recipientInfos, + } + innerContent, err := asn1.Marshal(envelope) + if err != nil { + return nil, err + } + + // Prepare outer payload structure + wrapper := contentInfo{ + ContentType: oidEnvelopedData, + Content: asn1.RawValue{Class: 2, Tag: 0, IsCompound: true, Bytes: innerContent}, + } + + return asn1.Marshal(wrapper) +} + +func marshalEncryptedContent(content []byte) asn1.RawValue { + asn1Content, _ := asn1.Marshal(content) + return asn1.RawValue{Tag: 0, Class: 2, Bytes: asn1Content, IsCompound: true} +} + +func encryptKey(key []byte, recipient *x509.Certificate) ([]byte, error) { + if pub := recipient.PublicKey.(*rsa.PublicKey); pub != nil { + return rsa.EncryptPKCS1v15(rand.Reader, pub, key) + } + return nil, ErrUnsupportedAlgorithm +} |