New answers tagged keys
2
Generally speaking: no, it is not OK. If you're going to encrypt any data at all with this key, you shouldn't reuse it to MAC other data. Using the same key for two purposes is bad practice and has often led to security problems in the practice.
Encrypting data without MACing it is also bad practice.
Instead, I recommend you use an "authenticated ...
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It depends on how you encrypt and mac.
If you can still choose then you should use an authenticated encryption with associated data mode (AEAD) like Galois/Counter Mode. If all data you want authenticated in a message has to be transmitted in the clear then just leave the encrypted part empty. These modes have the advantage that they were designed to use ...
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In entity authentication, the parties do not necessarily exchange a session key, but authenticate to each other by providing some proof related to their identites. For instance, if one party signs a challenge given by its partner, this party proves its identity.
Implicit key authentication merely guarantees that the partner (with whom you are talking right ...
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You never use RSA to encrypt large binary objects, since it's to expensive to do many calculations.
Instead, RSA is used in a key exchange or key transport protocol to send a key for a symmetric-key algorithm, such as AES (with a cipher chaining mode, such as CBC), which is then used to encrypt huge messages.
Also note that textbook RSA isn't secure. Some ...
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You asked several questions above. I will address one in specific that stands out to me, and that is your question about XORing the keys together. Your statement that they might both have the same character at the same location that would yield a null byte is disconcerting: passwords are not normally used directly as encryption keys.
Mathematically, a ...
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All too often I describe some process saying that "he" did something to "his" message,
and it makes sense in my own head, but no one else can figure out which of the several people involved that those pronouns refer to.
Or worse -- sometimes I say that "the message is encrypted", but I don't say who does it and with which key.
That's why all the good ...
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It doesn't seem like your goals are achievable.
You said you want Jim to be able to designate who can decrypt, but you don't want Jim to be able to decrypt himself. Those two requirements are not simultaneously satisfiable. If Jim can designate who can decrypt, Jim can designate himself (or, Jim can designate one of his friends/collaborators, Jane, who ...
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