openvpn-vulnkey disagrees with openssl-vulnkey

[James Roper]

Binary package hint: openvpn-blacklist

There are some keys that openssl-vulnkey says are comprised, that openvpn-vulnkey says are not compromised:

$ openvpn-vulnkey sample.key
Not blacklisted: #### sample.key
$ openssl-vulnkey sample.key
COMPROMISED: #### sample.key

I've hashed out some of the output because I'm not sure if leaving it in the bug report presents a security risk, but I can tell you that the hashed out data was different for each command (ie, openvpn-vulnkey printed out a different value to openssl-vulnkey).

Which one should be used and trusted when checking openvpn keys? openvpn itself is using openssl-vulnkey to verify whether keys are blacklisted (this has been reported as a bug in other places). The system administrator at my work ran openvpn-vulnkey against all the keys and is adamant that all our keys are safe. Meanwhile I can't start openvpn because it is using openssl-vulnkey to verify the key, which says its compromised. If openvpn-vulnkey is incorrectly reporting keys as not blacklisted, then this is a serious security issue. The other possibility is that openvpn is incorrectly using openssl-vulnkey.

The release of Ubuntu I am using is 8.04.
Package version is 0.1-0ubuntu0.8.04.1.

[Jamie Strandboge (jdstrand)]

Thank you for using Ubuntu and taking the time to report a bug. openvpn-vulnkey and openssl-vulnkey tests different types of keys. Specifically, openvpn-vulnkey checks openvpn shared keys as generated with 'openvpn --genkey --secret'. These key files are in a different format from files generated with the openssl command. On the other hand, openssl-vulnkey can check any SSL/TLS x509, CSR or RSA key. OpenVPN can be configured to use either shared keys, or traditional x509 certificates, and it will use openvpn-vulnkey or openssl-vulnkey depending on which type of key in use. For more information, please see 'man openssl-vulnkey' and 'man openvpn-vulnkey'.

[James Roper (jroper2-gmail)]

Thankyou for the speed of your response and the clear explanation.

[Seva Gluschenko (gvs-ya)]

# openvpn --config /etc/openvpn/openvpn.conf
Thu Jun 19 01:56:08 2008 OpenVPN 2.1_rc7 i486-pc-linux-gnu [SSL] [LZO2] [EPOLL] built on Jun 11 2008
Enter Private Key Password:
Thu Jun 19 01:56:10 2008 /usr/bin/openssl-vulnkey -q -b 1024 -m <modulus omitted>
Thu Jun 19 01:56:10 2008 ERROR: '/etc/ssl/private/privkey.pem' is a known vulnerable key. See 'man openssl-vulnkey' for details.
Thu Jun 19 01:56:10 2008 Exiting

by the way, openvpn.conf looks like
...
dev tun
client
nobind
ca /etc/ssl/certs/allCAs.pem
cert /etc/ssl/certs/XXX.pem
key /etc/ssl/private/privkey.pem
cipher AES-128-CBC
tls-client
...

I tried to make modulus from my privkey and pass it to openssl-vulnkey, and it reports that the key is not blacklisted. The sample output from /usr/share/openssl-blacklist/blacklist.RSA-* shows that vulnerable keys's modulus strings are significantly shorter than one produced from my key. What might be wrong with that thing? How can I correct openssl-vulnkey call or simply disable it?

The system is Ubuntu 8.04.1, openvpn-blacklist package is 0.1-0ubuntu0.8.04.1

[Jamie Strandboge (jdstrand)]

When using the '-m' option, you must pass the correct bit length and modulus string. You can find the modulus and bit length of your private key by using:

$ openssl rsa -modulus -text -in <private keyfile>
Private-Key: (1024 bit)
...
Modulus=E5FCB9EA68147B962AC4DC70CCB751AE27237D5C2073DA5119B61CB15FAE4A0451A46548983F000F8E5ABD3C34C1D2021834C08810314900997EC65F769E36612B8ECBF2DE3E3DAC4CA4246B33A933D4A639FE04ECE3D677DE0EF49BFCD3D77B133661E32BBEF6D103560883361A99ADA1D89779C0C0108EC3696D0A4C549F05
...

Proper invocation using the above example would look like:

$ openssl-vulnkey -b 1024 -m E5FCB9EA68147B962AC4DC70CCB751AE27237D5C2073DA5119B61CB15FAE4A0451A46548983F000F8E5ABD3C34C1D2021834C08810314900997EC65F769E36612B8ECBF2DE3E3DAC4CA4246B33A933D4A639FE04ECE3D677DE0EF49BFCD3D77B133661E32BBEF6D103560883361A99ADA1D89779C0C0108EC3696D0A4C549F05
COMPROMISED: 58dce70acfd4dc1a9d28722fc62edb8d30110778

The content of /usr/share/openssl-blacklist/blacklist.RSA-* are truncated hashes to save space, but openssl-vulnkey handles all of that for you. See 'man openssl-vulnkey' for details.

openssl-vulnkey is running correctly and the proper course of action is to regenerate your certificate/key pair because they use a known moduli and therefore your VPN traffic can easily be decrypted.

[freet15 (freet15)]

Seva Gluschenko , I have meet a some problem as you got, and I check the openssl-vulnkey , or cp /usr/sbin/openvpn-vulnkey to openssl-vulnkey, still not work. :( seriously~~

[Jamie Strandboge (jdstrand)]

openvpn-vulnkey and openssl-vulnkey are two separate programs that test different things. openssl-vulnkey checks openssl certificates, et al whereas openvpn-vulnkey checks *only* the shared key as generated with 'openvpn --genkey --secret'. They are not interchangeable.