I reported an insecure DKIM key to Deutsche Telekom / T-Systems.

[badkeys@infosec.exchange]

I reported an insecure DKIM key to Deutsche Telekom / T-Systems. They first asked me to further explain things (not sure why 'Here's your DKIM private key' needs more explanation, but whatever...). Then they told me it's out of scope for their bugbounty.

I guess then there's really no reason not to tell you: They have a 384 bit RSA DKIM key configured at: dkim._domainkey.t-systems.nl

384 bit RSA is... how shall I put it? I think 512 bit is the lowest RSA key size that was ever really used. 384 bit RSA is crackable in a few hours on a modern PC (using cado-nfs). The private key is:
-----BEGIN RSA PRIVATE KEY-----
MIHxAgEAAjEAtTliQYV2Xvx1OGkDyOL799BTFEuobY2dn2AgtiKCQgrh78NVK1JK
j0yRXgNnPpGBAgMBAAECMF0t+TBZUCi8xATSMij7VLTxv5Xi5OIXesNiXOKtYIRP
LkpYfR5PggaMScfbmqSssQIZAMwOhm9d7Y7Qi7I2j1AlYbiqdtqO54T7FQIZAONa
9dJFkC6lM3EPXR+0SZ4dqwwpiM0nvQIYYgz8thi5JK264ohq9sTvnu9yKvUN9I09
AhgfgMYZKcxtujRjkSZtMzUUNLYzzDmJe90CGDKwqcBI0v9ChaR8WHht+/chMdxj
7ez94w==
-----END RSA PRIVATE KEY-----

[benbe@social.chaotikum.org]

@badkeys

You had me at

-----BEGIN RSA PRIVATE KEY-----

[gerhardd@olching.social]

@badkeys

[q@glauca.space]

@badkeys You thought 384-bit was bad? I recently found a live, in daily use, 256-bit key in a, shall we say, large government entity that should know better (would rather not say much more publicly as its relevant to a paper under submission).

[momo@social.linux.pizza]

@badkeys
Do they accept mails from noncommercial mailservers at their nl branch or do they refuse them with "554 None/Bad Reputation" as the german branch does, unless the mail admin publishes full personal (!) contact infos on a webserver hosted on the smtp machine? Just asking, because THOSE guys behave like they wrote the SMTP RFCs all by themselves...

[dragonfrog@mastodon.sdf.org]

@badkeys
Looks like they've fixed it now (?)

The TXT record is now
"v=DKIM1; k=rsa; g=*; s=email; p=MEwwDQYJKoZIhvcNAQEBBQADOwAwOAIxALU5YkGFdl78dThpA8ji+/fQUxRLqG2NnZ9gILYigkIK4e/DVStSSo9MkV4DZz6RgQIDAQAB"

I really hope they generated a new key, and didn't just switch from publishing the private key to the corresponding public one...

[kkarhan@jorts.horse]

@momo @badkeys sadly this is being normalized today.

• #Microsoft literally demands people to self-d0x or they just silently drop all eMails, even replies to their customers.
  • And OFC neither @BNetzA nor @EUCommission did anything about this.

[buherator@infosec.place]

@badkeys My educated guess is they couldn't fit larger keys into their DNS records...

[wall_e@ioc.exchange]

@badkeys bruh

[millie@infosec.exchange]

@dragonfrog @badkeys Most people might not be fluent in base64-encoded ASN.1, but a trained eye can see that it's the same key.

Hint: A sufficiently strong RSA key cannot possibly be that short, and you know it's a DER-encoded pubkey because it starts with "ME" and ends with "AQAB" (0x10001, common RSA public exponent)

[mcr314@todon.nl]

@buherator @badkeys No, they thought they were generating an ECDSA key, for which a 256 or 384 bit would be strong. But, they didn't provide the right arguments, and wound up with RSA. I think the OP posted the private key that they were able to crack trivially.

[dragonfrog@mastodon.sdf.org]

@millie @badkeys
Oh gosh, so they've removed the private key, but it's still the public key that goes with a private key that they already published.

A sound as if a thousand faces rested in a thousand palms, and a thousand IT people sighed heavily...

[millie@infosec.exchange]

@dragonfrog @badkeys No, the private key was never published by t-systems, but it's so weak that it's very easy to crack. OP cracked and published the private key.

[buherator@infosec.place]

@mcr314 @badkeys Source? I doubt someone who makes a mistake like this knows what ECDSA is.

[dragonfrog@mastodon.sdf.org]

@millie @badkeys thank you, I get it now. Iguess I'm having a slow day!

[irelephant@app.wafrn.net]

@badkeys@infosec.exchange

send an email coming from them.

[bebef@mastodon.social]

@kkarhan @momo @badkeys @BNetzA @EUCommission Had the same issue just recently. I wonder how this can even be legal.

I wanted to ask a lawyer about this, but never came around doing so.

[16af93@wetdry.world]

@q @badkeys BSI at it again?

[q@glauca.space]

@16af93 @badkeys for once, its not the Germans

[16af93@wetdry.world]

@q @badkeys