Given that this is asymmetric cryptography with private/public key, I am not sure if reduced bit length is breakable easier than longer keys. I understand that the key population is reduced (hence randomness, hence brute force) however, I am still wondering, does this mean it is easily breakable? Are there any studies/research/cryptanalysis performed to measure what this mean?

The site I am referring to here is web.Whatsapp.com

India wants social media sites such as Whatsapp to make the content accessible by Government (because of hatred spread on social media that led to people being lynched!). Is it possible that the public key size is purposefully reduced to accommodate this?

I got a VPN through US and verified it is 256 bits for accessing in US too. So, is it possible that WhatsApp is not as secure as we think?

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    The public key crypto being used by WhatsApp web is Curve25519. – defalt Dec 30 '18 at 6:43
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    Generally, to get 128 bit security for ECC, you need approximately double the key size, or 256 bits for the public key. To get the same for non-ECC asymmetric cryptography such as RSA, you need around 3072 bits. You really can't compare them. Also, if WhatsApp uses Curve25519, then it is sufficiently secure and has approximately 116 bits of effective security (i.e. equivalent to a 116-bit symmetric key). – forest Dec 30 '18 at 8:28
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    use keylength.com/en/compare – kelalaka Dec 30 '18 at 22:28
  • @default - please advise a tool to figure out the crypto used by Whatsapp. I am just using Wormly at this time. Thanks much! – tazz Dec 31 '18 at 8:35
  • WhatsApp client uses Signal protocol as documented by them. WhatsApp web uses standard TLS connection to communicate with the device. For WhatsAppp web you can look up the communication in wireshark. – defalt Dec 31 '18 at 21:01

In short, 256-bit public key is from ECC, i.e. elliptic curve cryptography.

The 1024-bit public key refers to bit length of the RSA modulus N.

Now we are at late 2018, the best practice is a 2048-bit or higher modulus.

You can check https://en.wikipedia.org/wiki/Key_size for a detailed explanation regarding to key size.

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    2048 bit is the minimum bit size even in 2018, so I would not call that best practice. It of course depends on the application, but if you can use a 4096 bit key then I would not hesitate to do so. More information at keylength.com – Maarten Bodewes Nov 3 '19 at 0:19
  • @MaartenBodewes Thats fair. Thanks for point it out – 9f241e21 Nov 4 '19 at 7:41

It's an up-to-date website using elliptic curve cryptography (ECC). ECC key sizes are not directly comparable with RSA, and a 256-bit key is more than enough for security -- 112-bit is the most that has ever been cracked. It's equivalent to a 3072-bit RSA key.

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