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Error when connecting Power Automate to SFTP on AWS Transfer Family: Server HMAC algorithm not found

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Posted on by stephen1

Hi,

I'm attempting to use Microsoft Power Automate to connect to an AWS SFTP instance (Transfer Family). The SFTP host is working in that I can connect to it using the Linux sftp command line client.

When attempting to connect using MS PA, I get this error: Server HMAC algorithm not found

The AWS log shows this:

{

"activity-type": "KEX_FAILURE",

"source-ip": "xxxx",

"resource-arn": "arn:aws:transfer:regions-xxxxxx:server/xxxx",

"message": "no matching host key type found",

"kex": "ssh-rsa,ssh-dss,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521"

}

Does anyone know what the problem might be?

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theblisster 5 on at

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Exact same problem here! please help!

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stephen1 11 on at

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It seems the problem was with the key. The private key needs to start with -----BEGIN RSA PRIVATE KEY----- (not -----BEGIN OPENSSH PRIVATE KEY-----
) for this to work.

To create a key like this, follow these two steps:

ssh-keygen -t rsa -b 4096 -f my_rsa_key
ssh-keygen -p -f my_rsa_key -m pem (then use that key to connect using power automate private key)

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Yugendiran 2 on at

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Exact same problem. Any solution?

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tgaki 2 on at

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We were having similar issues with a customer using Power Automate. After some digging into both sides of the issue, I found that the Transfer Security Policy on the AWS Transfer Family configuration was too new for Power Automate to connect. Unfortunately it looks like there's absolutely no control over this from the client perspective with Power Automate, so the only solution for this to work is to downgrade the Transfer Security Policy to at least "TransferSecurityPolicy-2020-06" on the Transfer Family SFTP instance.

Additionally, stephen1's response is correct as well in that the key needs to be in RSA PRIVATE KEY format, not OPENSSH.

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