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avatar Crypto

Is this AES GCM + asymmetric schema secure?

cn flag
blockmined

I want to use the asymmetric encription offered by a tool to encrypt my files and I would like to know if the following encryption process works, regardless of perhaps not optimal use.

  • Generate a 32-bytes-random-key inside the browser with window.crypto.getRandomValues

  • use sjcl crypto library for:

    • choosing AES algorythm cipher.aes
    • generating 4 words random IV vector random.randomWords(4, 0)
    • encrypting a file in GCM mode mode.gcm.encrypt (tag 128 bits)
    • concating IV and encrypted output producing the binaryFile1

  • use NaCl Networking and Cryptography library, through a tool that implements ECIES, for:

    • generating an encryptionKeypair using nacl.box.keyPair.fromSecretKey
    • encrypting the above 32-bytes-random-key with the ephemeralPublicKey (using the x25519 part of the schema x25519-xsalsa20-poly1305) producing the binaryFile2, a bundle containing the encrypted AES key and, among other metadata, the ephemeralPublicKey.

  • concat binaryFile2 + a-separator + binaryFile1 producing finalBinaryFile

  • keep the finalBinaryFile on the cloud until it is necessary to download it and then decrypt it through the reverse process using the secretKey I own.

To encrypt the files I could directly use the symmetric key keeping it safe but I would like to use a DB of shared static public keys, whose trustness I can assume valid.

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kelalaka avatar
in flag
kelalaka
What is the question?
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cn flag
blockmined
I made the question explicit in the title. Thank you.
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kelalaka avatar
in flag
kelalaka
Why don't you use well-maintained programs like Veracrypt or libraries like the [age](https://github.com/FiloSottile/age) (_age is a simple, modern and secure file encryption tool, format, and Go library_.)
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Maarten Bodewes avatar
in flag
Maarten Bodewes
Complete reviews of cyptographic protocols and schemes is off topic. Using ECIES to encrypt a secret key is a bit spurious; you could use the key agreement part itself to establish a key. Of course, you'd also need to send the ephemeral public key for ECIES, something that is missing in your protocol. I don't see how you've established the static key pair of the receiver or how that public key is trusted, so the description is certainly not without fault nor complete.
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cn flag
blockmined
Thank you for your remarks Maarten. Actually I forgot to mention that in the `binaryFile2` there is also the ephemeral publick key so I will update the question. I am aware that I am asking about the validity regardless to the process of registration of the static key pair and relative trustness.
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Score:2
SAI Peregrinus avatar Crypto
si flag
SAI Peregrinus

NaCL provides a set of crypto_box methods which do this all in one go. Libsodium provides an even easier set of crypto_box_easy methods.

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cn flag
blockmined
Thank you for your suggestion, My implementation has to be in javascript so I am just using a wrap of NaCl set that offers and manages key pair generations.
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SAI Peregrinus avatar
si flag
SAI Peregrinus
There are JS bindings for libsodium as well.
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