func commonDecrypt()

in v3/materials/kms_keyring.go [180:216]
33 lines of code
6 McCabe index (conditional complexity)

func commonDecrypt(ctx context.Context, materials *DecryptionMaterials, encryptedDataKey DataKey, kmsKeyId *string, matDesc MaterialDescription, kmsClient KmsAPIClient) (*CryptographicMaterials, error) {
	if matDesc != nil {
		if v, ok := matDesc[kmsAWSCEKContextKey]; !ok {
			return nil, fmt.Errorf("required key %v is missing from encryption context", kmsAWSCEKContextKey)
		} else if v != materials.ContentAlgorithm {
			return nil, fmt.Errorf(kmsMismatchCEKAlg)
		}
	}

	in := &kms.DecryptInput{
		EncryptionContext: materials.MaterialDescription,
		CiphertextBlob:    encryptedDataKey.EncryptedDataKey,
		KeyId:             kmsKeyId,
	}

	grantTokens := ctx.Value(GrantTokens)
	if grantTokens != nil {
		in.GrantTokens = grantTokens.([]string)
	}

	out, err := kmsClient.Decrypt(ctx, in)
	if err != nil {
		return nil, err
	}

	materials.DataKey.KeyMaterial = out.Plaintext
	cryptoMaterials := &CryptographicMaterials{
		Key:                 out.Plaintext,
		IV:                  materials.ContentIV,
		KeyringAlgorithm:    materials.DataKey.DataKeyAlgorithm,
		CEKAlgorithm:        materials.ContentAlgorithm,
		TagLength:           materials.TagLength,
		MaterialDescription: materials.MaterialDescription,
		EncryptedKey:        materials.DataKey.EncryptedDataKey,
	}
	return cryptoMaterials, nil
}