From 1adcf5689048887cc05c0a600235249e606423d1 Mon Sep 17 00:00:00 2001
From: Gilbert Chen <gchen@acrosync.com>
Date: Mon, 8 Jun 2020 11:24:20 -0400
Subject: [PATCH] Add an SFTP backend that supports more ciphers and kex
 algorithms.

"sftpc://" supports all algorithms implemented in golang.org/x/crypto/ssh,
especially including those weak ones that are excluded from the defaults.
---
 src/duplicacy_sftpstorage.go | 21 +++++++++++++++++----
 src/duplicacy_storage.go     |  4 ++--
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/duplicacy_sftpstorage.go b/src/duplicacy_sftpstorage.go
index 06bcd50..5f741ee 100644
--- a/src/duplicacy_sftpstorage.go
+++ b/src/duplicacy_sftpstorage.go
@@ -43,10 +43,10 @@ func CreateSFTPStorageWithPassword(server string, port int, username string, sto
 		return nil
 	}
 
-	return CreateSFTPStorage(server, port, username, storageDir, minimumNesting, authMethods, hostKeyCallback, threads)
+	return CreateSFTPStorage(false, server, port, username, storageDir, minimumNesting, authMethods, hostKeyCallback, threads)
 }
 
-func CreateSFTPStorage(server string, port int, username string, storageDir string, minimumNesting int,
+func CreateSFTPStorage(compatibilityMode bool, server string, port int, username string, storageDir string, minimumNesting int,
 	authMethods []ssh.AuthMethod,
 	hostKeyCallback func(hostname string, remote net.Addr,
 		key ssh.PublicKey) error, threads int) (storage *SFTPStorage, err error) {
@@ -57,8 +57,21 @@ func CreateSFTPStorage(server string, port int, username string, storageDir stri
 		HostKeyCallback: hostKeyCallback,
 	}
 
-	if server == "sftp.hidrive.strato.com" {
-		sftpConfig.Ciphers = []string{"aes128-ctr", "aes256-ctr"}
+	if compatibilityMode {
+		sftpConfig.Ciphers = []string{
+			"aes128-ctr", "aes192-ctr", "aes256-ctr",
+			"aes128-gcm@openssh.com",
+			"chacha20-poly1305@openssh.com",
+			"arcfour256", "arcfour128", "arcfour",
+			"aes128-cbc",
+			"3des-cbc",
+		}
+		sftpConfig.KeyExchanges = [] string {
+			"curve25519-sha256@libssh.org",
+			"ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521",
+			"diffie-hellman-group1-sha1", "diffie-hellman-group14-sha1",
+			"diffie-hellman-group-exchange-sha1", "diffie-hellman-group-exchange-sha256",
+		}
 	}
 
 	serverAddress := fmt.Sprintf("%s:%d", server, port)
diff --git a/src/duplicacy_storage.go b/src/duplicacy_storage.go
index 33ed6c4..c060062 100644
--- a/src/duplicacy_storage.go
+++ b/src/duplicacy_storage.go
@@ -268,7 +268,7 @@ func CreateStorage(preference Preference, resetPassword bool, threads int) (stor
 	if matched == nil {
 		LOG_ERROR("STORAGE_CREATE", "Unrecognizable storage URL: %s", storageURL)
 		return nil
-	} else if matched[1] == "sftp" {
+	} else if matched[1] == "sftp" || matched[1] == "sftpc" {
 		server := matched[3]
 		username := matched[2]
 		storageDir := matched[5]
@@ -440,7 +440,7 @@ func CreateStorage(preference Preference, resetPassword bool, threads int) (stor
 			return checkHostKey(hostname, remote, key)
 		}
 
-		sftpStorage, err := CreateSFTPStorage(server, port, username, storageDir, 2, authMethods, hostKeyChecker, threads)
+		sftpStorage, err := CreateSFTPStorage(matched[1] == "sftpc", server, port, username, storageDir, 2, authMethods, hostKeyChecker, threads)
 		if err != nil {
 			LOG_ERROR("STORAGE_CREATE", "Failed to load the SFTP storage at %s: %v", storageURL, err)
 			return nil