Hot answers tagged signature
5
Yes. Any good standard digital signature algorithm will be secure in this setting.
Digital signature algorithms are designed to be secure against chosen-message attacks, where the attacker can choose any set of messages and learn the signatures on those messages; the security of the signature scheme means that this doesn't help the attacker at all. This ...
3
"Efficient, Compromise Resilient and Append-only Cryptographic
Schemes for Secure Audit Logging" (PDF) gives a publicly verifiable approach that allows
fine-grained verification, but it is in the Random Oracle Model.
The Simple Method:
The verifier and logger start with a seed for a forward-secure pseudo-random number generator.
To denote a valid ending ...
2
First and foremost: it is a bad idea to invent a method to sign or encrypt with RSA (or any crypto). Standards like PKCS#1 or ISO/IEC 9796-2 are here for that purpose, and even these occasionally have more or less subtle flaws.
Given comments, I'll assume that the question is about an RSA encryption scheme enciphering message $M$ into $(M||S)^e\bmod N$, and ...
1
Edit: You've clarified in the comments that confidentiality of the logfile's contents is important.
Given an AEAD function $C = E_k(iv, plaintext, aad)$, a safe construct is
$$
C = E_k(iv, contents, filename).
$$
There is no need to include either the key or the IV in the additional authenticated data, and I would recommend against doing so. It is ...
1
The primary problem with encrypt-then-sign (signing the ciphertext) relates to the difference between signing for the purpose of assigning responsibility vs for the purpose of taking credit. Encrypt-then-sign is OK for the former but not for the latter. The issue is quite subtle.
In particular, in your protocol, the recipient has no reason to believe the ...
1
I'm thinking there's a third potential solution. Each time you close a log file, you could append the name of the next new log file, timestamp it, then sign the log file. When it is time to create a new log file, you would read the previous log file, validate the signature, validate the time stamp, read the new log file name, and create it. You'd ...
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