mirror of
https://github.com/emmansun/gmsm.git
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89 lines
2.6 KiB
Go
89 lines
2.6 KiB
Go
package pkcs7
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import (
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"bytes"
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"crypto"
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"crypto/rand"
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"encoding/asn1"
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"errors"
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"github.com/emmansun/gmsm/pkcs"
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"github.com/emmansun/gmsm/smx509"
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)
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// ErrUnsupportedAlgorithm tells you when our quick dev assumptions have failed
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var ErrUnsupportedAlgorithm = errors.New("pkcs7: cannot decrypt data: only RSA, SM2, DES, DES-EDE3, AES and SM4 supported")
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// ErrNotEncryptedContent is returned when attempting to Decrypt data that is not encrypted data
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var ErrNotEncryptedContent = errors.New("pkcs7: content data is NOT a decryptable data type")
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type decryptable interface {
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GetRecipient(cert *smx509.Certificate) *recipientInfo
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GetEncryptedContentInfo() *encryptedContentInfo
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}
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// Decrypt decrypts encrypted content info for recipient cert and private key
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func (p7 *PKCS7) Decrypt(cert *smx509.Certificate, pkey crypto.PrivateKey) ([]byte, error) {
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decryptableData, ok := p7.raw.(decryptable)
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if !ok {
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return nil, ErrNotEncryptedContent
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}
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recipient := decryptableData.GetRecipient(cert)
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if recipient == nil {
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return nil, errors.New("pkcs7: no enveloped recipient for provided certificate")
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}
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switch pkey := pkey.(type) {
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case crypto.Decrypter:
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// Generic case to handle anything that provides the crypto.Decrypter interface.
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contentKey, err := pkey.Decrypt(rand.Reader, recipient.EncryptedKey, nil)
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if err != nil {
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return nil, err
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}
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return decryptableData.GetEncryptedContentInfo().decrypt(contentKey)
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}
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return nil, ErrUnsupportedAlgorithm
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}
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// DecryptUsingPSK decrypts encrypted data using caller provided
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// pre-shared secret
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func (p7 *PKCS7) DecryptUsingPSK(key []byte) ([]byte, error) {
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data, ok := p7.raw.(encryptedData)
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if !ok {
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return nil, ErrNotEncryptedContent
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}
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return data.EncryptedContentInfo.decrypt(key)
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}
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func (eci encryptedContentInfo) getCiphertext() (ciphertext []byte) {
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// EncryptedContent can either be constructed of multple OCTET STRINGs
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// or _be_ a tagged OCTET STRING
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if eci.EncryptedContent.IsCompound {
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// Complex case to concat all of the children OCTET STRINGs
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var buf bytes.Buffer
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cypherbytes := eci.EncryptedContent.Bytes
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for {
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var part []byte
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cypherbytes, _ = asn1.Unmarshal(cypherbytes, &part)
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buf.Write(part)
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if cypherbytes == nil {
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break
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}
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}
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ciphertext = buf.Bytes()
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} else {
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// Simple case, the bytes _are_ the cyphertext
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ciphertext = eci.EncryptedContent.Bytes
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}
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return
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}
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func (eci encryptedContentInfo) decrypt(key []byte) ([]byte, error) {
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alg := eci.ContentEncryptionAlgorithm.Algorithm
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cipher, err := pkcs.GetCipher(alg)
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if err != nil {
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return nil, ErrUnsupportedAlgorithm
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}
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return cipher.Decrypt(key, &eci.ContentEncryptionAlgorithm.Parameters, eci.getCiphertext())
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}
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