Need to create RSA key with forced exponent 35 and using ssh-keygen

Hello,

I have a rather unusual problem. I will spare you the details, but on one CentOS 7 server I need to create a new RSA key. We would normally use this command:

ssh-keygen -h -f /etc/ssh/ssh_host_rsa_key

However, this command creates the key with Public Exponent 65537 (0x10001). But for compatibility reasons with one application I need the key to be created with Public Exponent 35 (0x23), just as was the default with CentOS 5 and CentOS 6.

Any help would be appreciated.

Thanks!
tomfraAsked:
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gheistCommented:
I see rhel5 and rhel6 using 65537 by default.
You can read on how 65537 became default 8 years ago, right before RHEL5 was released.
https://en.wikipedia.org/wiki/RSA_%28cryptosystem%29#Faulty_key_generation

If you really insist on generating weak keys you can use openssl genrsa which supports them.
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tomfraAuthor Commented:
Well, on CentOS 6, even updated to the latest version, the following command:

ssh-keygen -h -f /etc/ssh/ssh_host_rsa_key

generates the key with exponent 35 (0x23). I need to know the exact command to replicate this behavior on CentOS 7 before one application we use is updated and distributed to all users.
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gheistCommented:
Horrible... They keep old vulnerability alive.

As I said - openssl genrsa generates exactly same keys
Write "openssl genrsa --help" to learn more
If you cannot find parameter you can generate key on old systems. Dont forget to use /dev/zero as RNG for full security effect in this case.
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tomfraAuthor Commented:
Thanks for the information, accepting your solution.
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