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When the TScSSHChannel.Direct property is set to True, then on calling TScSSHChannel.Connect a new channel with server is created, and respectively the TScSSHServer.BeforeChannelConnect event is raised.
If the TScSSHChannel.Direct property is False, then the component starts listening to the SourcePort on the local host, and creates the new channel only when someone connects to this port. Accordingly, at that moment the TScSSHServer.BeforeChannelConnect event is raised.
In the btSConnectClick method of our SSHClient demo, a connection to TScSSHChannel.SourcePort is emulated to demonstrate the above functionality. In practice, this can be applied when, for example, you already have a client working with a database, and it needs to implement connection via a protected channel using SSH. In such case, you run TScSSHChannel with Direct := False, that listens to the specified port - and the database client now connects to this port. At this, TScSSHChannel creates a protected channel with SSH server and transfers database client data over this channel. SSH server decrypts the data - and transfers it over unprotected channel.

In asymmetric encryption, (RSA or DSA types) two keys are used. The private key is used for data decryption and signing, the public key is used for data encrypting.
The message cannot be decrypted by anyone who does not possess the matching private key. This is used in an attempt to ensure confidentiality.

It is good to see that the problem has been solved.

Use the TScCertificate.VerifySign function to verify whether the signature is correct (it is named decrypting the signature) for specified data.
You can learn more about this here: https://en.wikipedia.org/wiki/Public-key_cryptography

nathschu_sel wrote:I experienced this doing low-volume transfers (serial port / terminal forwarding with ymodem data).
...

We can not reproduce the problem. Please, try to compose a small sample to demonstrate the problem and send it to dmitryg*devart*com.

BlueGI wrote:Recently we upgraded to version 6.5.8 05-May-15. I cannot recall if we had any previous version issues, but lately we are having trouble uploading files larger than 1 GB. It seems that once it reaches 1020MB (or thereabouts), it stops and waits for the TimeOut period. Then an exception of "Timeout expired, session have not responded" is returned.

We have reproduced this problem and fixed it. This fix will be included in the next SecureBridge build.

We are sorry for the delay . The next SecureBridge build will be released at the beginning of the next week.

If any other questions come up, please contact us.

If any other questions come up, please contact me.

To solve the problem try to turn the Allow service to interact with desktop option on. For that perform the next steps:
1.In the Services tool, click the service that you want to start, and then click Properties.
2. Right-click the Log On tab, and then click to select the Allow service to interact with desktop check box.
3. Click OK to exit the Properties dialog box.

UserIdx64 wrote:2. How to import Public & Private keys which generated from PuttyGen?

The fact is that PuTTY saves keys in its own format. You should export your keys in the OpenSSH or SSH2 format.
For that you should load your private key in PuTTY Key Generator, and export it to any available format using the Conversions menu.
After that you should import this key in TScStorage using the TScKey.ImportFrom method.

UserIdx64 wrote:1. Can SB accept SSH Server Public key automatically (Do not use "Import Server key" functionality)?

TScSSHClient doesn't accept a server public key automatically, because it breaks security principles.

1. Thank you for the information. We have reproduced this problem and fixed it. This fix will be included in the next SecureBridge build.

2. To solve the problem try starting sshserver.exe with administrative rights.

We have investigated the problem and haven't found any issues in SecureBridge to be the reason for this error. But we have discovered the same behaviour with other non-visual components, like TDataSource.
Therefore it seems, that the described issue belongs to Lazarus, not to SecureBridge components.

It seems, that SFTP Server doesn't have access rights to a directory. Try to download a file step by step without using the DownloadFile method. Please follow the steps below:
1. Establish SFTP connection using the TScSFTPClient.Initialize method.
2. Open a remote file by the OpenFile method.
3. Retrieve file attributes by the RetrieveAttributesByHandle method.
4. Read the data using the ReadFile method in a loop until the file download is completed.