SCP with Resume Feature

Demi Marie Obenour demiobenour at
Sun Apr 4 10:10:42 AEST 2021

On 4/1/21 1:50 PM, rapier wrote:
> Howdy all,
> I know development on SCP is discouraged but being that it's still in wide use
> I thought I would do some work some of my users have been asking for and allow
> SCP to resume from a partial transfer.

Would it be possible to instead reimplement SCP in terms of SFTP, and then add
this feature to SFTP?  My understanding is that such a re-implementation is
something many people have wanted for quite a while.

Of course, this might very well be out of scope for the project, which would
be fine.

> When enabled the resume function will compare the source and target files. The
> source host will and target host will pass MD5 hashes back and forth in order
> to compare the hash of the file fragment on the target and the file up to the
> length of the source file. If these hashes match the source will seek to the
> appropriate byte position and start sending the rest of the file. This will
> then be appended to the target.

I suggest using a better hash than MD5, which is considered broken.  Blake2b is
both faster and much more secure.


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