I was looking at the SSL certificates of various major web sites and I notice that Google is using a 256-bit SSL certificate:

Common Name = *.google.com
Subject Alternative Names = *.google.com, *.android.com, ... urchin.com, www.goo.gl, youtu.be, youtube.com, youtubeeducation.com
Serial Number = 0FC98430DAD8C2FD
SHA1 Thumbprint = D8B657CD0DB96AC349B3491D229285BD18F6C7FA
Key Length = 256
Signature algorithm = SHA256 + RSA (excellent)

I can't believe that Google would use a cert that is not secure, so there must be an explanation.

Is there something special about the way Google is using this that makes it secure? Or am I being too pessimistic about the security of 256 bit SSL certs?


Some further examination of this certificate and I understand. Most large sites are using 2048-bit RSA keys.

Google is using a 256-bit EC (elliptical curve) key. EC keys larger than 130 bits are still considered secure.

About 130-bit EC keys being secure:

Here is a public challenge to break one: https://ecc-challenge.info/ 160-bit EC key being equivalent to 1024 RSA key: https://www.globalsign.com/en/blog/elliptic-curve-cryptography/

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    $\begingroup$ This is actually false, the signature length is correctly indicated as 2048 bits (i.e. 256 bytes). The signature algorithm is RSA (as stated in the quote in your own question). $\endgroup$ – Aleph Apr 7 '17 at 17:33
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    $\begingroup$ Looks like both are supported. But in the quote in your question, the signature algorithm is listed as RSA in any case. $\endgroup$ – Aleph Apr 7 '17 at 17:39
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    $\begingroup$ This certificate uses an EC 256-bit key. The signature algorithm is what was used to sign this CERT. That means (i think) the certificate authority used an RSA key. This SO thread explains: security.stackexchange.com/questions/141661/… $\endgroup$ – Rafael Baptista Apr 7 '17 at 17:45
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    $\begingroup$ This kind of discussion is easy to avoid: just add the PEM or base 64 encoded certificate to your question. $\endgroup$ – Maarten Bodewes Apr 7 '17 at 23:23
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    $\begingroup$ @Aleph From what I know, Google dynamically either presents an ECC certificate or an RSA certificate to the end user, which is also why they can offer ECDSA and RSA based cipher suites at the same time. $\endgroup$ – SEJPM Apr 9 '17 at 13:26

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