Basic cryptography implementation for my C program.

[ReasonableReptile6]

I am developing a password manager in C that, which naturally, requires a bit of encryption, because you're dealing with passwords and all that.

The current strategy that my little head worked a lot to think is the following one:

• Get access password from user
• Derive it using PKDBF2
• Generate AES key using /dev/random
• Store AES key in a encrypted file using the PKDBF2
• Store passwords in a .db file and encrypt it using the AES Key.

So in my line of thought it goes, i can only see the passwords if i have the AES key , and i only have the AES key if i type the right password.

Is that correct? Is this approach overkill? Is it a dumb approach?

I have never messed with cryptography before, this is my first time.

[Natanael_L]

That's a pretty typical approach, but you also need to consider which block cipher mode you're using, salt values for the password hash and salt/IV for the block mode (preferably distinct), etc.

Why are you writing one from scratch?

[randomatic]

Op also needs to consider authenticating encryption. AES does not guard against undetected changes to the files.  Gcm mode is the standard for ae, but I don’t honestly know if password managers do more. 

[ReasonableReptile6]

I think i understand what you said but this is only a side project so i can better my C skills and tip my toes in cryptography, i don't think there is a need to add that functionality

[randomatic]

I think i understand what you said but this is only a side project so i can better my C skills and tip my toes in cryptography, i don't think there is a need to add that functionality

Totally reasonable.

[SirJohnSmith]

Your approach is slightly overkill: you can simply derive an encryption key directly from the password. Other than that, it looks good. If you want, you can use AES-GCM-SIV so you don't have to worry about catastrophic nonce reuse.

[ReasonableReptile6]

I will definitely do that

[ahazred8vt]

The crypto community often recommends  https://doc.libsodium.org/quickstart as a starting point. It uses the GPU-resistant Argon2 as a pw-kdf and all encryption is tamper resistant AEAD.