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I am using Argon2 to convert an ECDH exchange result into the correct format for AES-256 encryption. However the library that I am using for Argon2 requires a salt. Are there any weaknesses of using a static, hard-coded salt for the Argon2 key format conversion?

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  • $\begingroup$ Would rainbow tables be constructed for SECP521r1 shared secrets?? If so, what would the salt length recommendation be? $\endgroup$ – SamG101 Sep 9 at 16:02
  • $\begingroup$ a shared secret does not need a high work factor KDF to get you a cipher key, you can use a single iteration of a 256-bit hash, or use a 512-bit hash such as SHA-512 if you need additional key material, such as an HMAC key $\endgroup$ – Richie Frame Sep 9 at 23:21

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