github.com/trustbloc/kms-go@v1.1.2/crypto/tinkcrypto/primitive/composite/ecdh/subtle/ecdh_aes_aead_composite_decrypt.go (about)

     1  /*
     2  Copyright SecureKey Technologies Inc. All Rights Reserved.
     3  
     4  SPDX-License-Identifier: Apache-2.0
     5  */
     6  
     7  package subtle
     8  
     9  import (
    10  	"encoding/json"
    11  	"fmt"
    12  
    13  	"github.com/trustbloc/kms-go/crypto/tinkcrypto/primitive/composite"
    14  )
    15  
    16  // package subtle provides the core crypto primitives to be used by ECDH composite primitives. It is intended for
    17  // internal use only.
    18  
    19  // ECDHAEADCompositeDecrypt is an instance of AES-GCM decryption in the context of ECDH/concat kdf WK of CEK
    20  // and AEAD content decryption.
    21  type ECDHAEADCompositeDecrypt struct {
    22  	encHelper composite.EncrypterHelper
    23  	cek       []byte
    24  }
    25  
    26  // NewECDHAEADCompositeDecrypt returns ECDH composite decryption construct with Concat KDF/ECDH-ES key unwrapping
    27  // and AEAD payload decryption.
    28  func NewECDHAEADCompositeDecrypt(encHelper composite.EncrypterHelper, cek []byte) *ECDHAEADCompositeDecrypt {
    29  	return &ECDHAEADCompositeDecrypt{
    30  		encHelper: encHelper,
    31  		cek:       cek,
    32  	}
    33  }
    34  
    35  // Decrypt using composite ECDH-ES with a Concat KDF key unwrap and AEAD content decryption.
    36  func (d *ECDHAEADCompositeDecrypt) Decrypt(ciphertext, aad []byte) ([]byte, error) {
    37  	encData := new(composite.EncryptedData)
    38  
    39  	err := json.Unmarshal(ciphertext, encData)
    40  	if err != nil {
    41  		return nil, err
    42  	}
    43  
    44  	if d.cek == nil {
    45  		return nil, fmt.Errorf("ecdh decrypt: missing cek")
    46  	}
    47  
    48  	aead, err := d.encHelper.GetAEAD(d.cek)
    49  	if err != nil {
    50  		return nil, err
    51  	}
    52  
    53  	finalCT := d.encHelper.BuildDecData(encData)
    54  
    55  	return aead.Decrypt(finalCT, aad)
    56  }