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    Home Unlabelled Cryptography An idea for a public-key cryptosystem. I need some constructive criticism.

    Cryptography An idea for a public-key cryptosystem. I need some constructive criticism.

    December 03, 2017

    Cryptography An idea for a public-key cryptosystem. I need some constructive criticism.

    An idea for a public-key cryptosystem. I need some constructive criticism.

    Posted: 02 Dec 2017 07:04 AM PST

    Are two layers of MAC required for this cryptosystem?

    Posted: 02 Dec 2017 01:09 PM PST

    A. General message encryption

    1. There is a payload to be delivered to 1..N interlocutors
    2. A random symmetric encryption key is generated
    3. The payload is symmetrically encrypted with the symmetric encryption key
    4. The payload ciphertext and the symmetric encryption key have a MAC generated on them

    B. Individual key encryption

    1. ECDH secret derivation protocol is used with N key pairs to generate N shared secrets
    2. Copies of the randomly generated symmetric encryption key from A2, are symmetrically encrypted with the outputs of B1 (one per interlocutor)
    3. ????

    Do I need to generate N MACs on the ECDH secrets and the symmetrically encrypted symmetric key from step B2? Or is the MAC on the payload and the plaintext symmetric encryption key from step A4 sufficient?

    Finally, the resultant values are composed into a message that can be decrypted by the holders of the associated N ECDH private keys.

    My intuition is that only the original MAC on the plaintext symmetric encryption key and the payload ciphertext is required, and that there doesn't need to be a MAC on the ciphertext symmetric encryption key and the output of ECDH that was used to symmetrically encrypt it. I'm not sure though.

    submitted by /u/the_murz
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    Having trouble finding the algorithm used.

    Posted: 02 Dec 2017 03:11 PM PST

    First off, I don't think this belongs in /r/codes, but I'm not sure it belongs here either. If you can direct me to a better place, please do.

    I'm trying to decipher some ciphertext that claims to be in ARC4. While I know this is weak crypto, the issue isn't in finding the key, it's that with a known key, the plaintext isn't matching. I have the ciphertext, and the key used to create it, but not the plaintext. As far as I know, all three examples should decipher into the same plaintext, but I don't know what that is. ( I think it should start with 69, but not sure. )

    Help wanted, or if it's very clearly not ARC4, guidance in how to locate what was used. This isn't a challenge or homework, it's part of a programming issue where I have most of the parts, but not all.

    Key: c4ce5570c1078107

    Msg: b3 98 37 bf f7 d6 4a b2 d1 3c a3 3c b8 b1 50 4f 27 a1 8c 8b 40 39 e3 bd 4b 16 f0 33 71 7c 5a d8 3a ec ed 6a 14 30 a7

    Key: bed0e1ad2685c811

    Msg: bf a5 c6 02 e7 1e c5 61 aa eb 3b 5a e3 de e0 ae 60 e5 5d de 30 26 e8 af c1 a4 8f 7d 5b 51 22 f1 fc bb d3 bf a7 65 86

    Key: d1b4e738c519eb80

    Msg: 0e c9 e8 94 55 8f b2 d7 62 c6 f0 61 43 83 58 e4 c9 c5 0c 57 3a 20 29 a8 f8 a4 85 62 d0 54 a4 26 f7 a1 a5 16 87 3d cb

    submitted by /u/drazisil
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    Getting started in Blockchain security

    Posted: 02 Dec 2017 06:49 AM PST

    As text title, I want to dig in blockchain security (from attack view). Any suggestion for me getting started in this field.

    submitted by /u/duongkai
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