Is OpenSSL enc using AES-256-CBC to encrypt large files safe?

henderson

10/12/22, 10:35 AM

I first generate a keyfile with openssl rand -hex 64 -out keyfile.

I then encrypt the file with openssl enc -aes-256-cbc -salt -in large_file.zip -out large_encrypted.bin -pass file:./keyfile.

I am encrypting files sized anywhere from a few bytes to 1TB. I will be using this in a simple bash script.

Is this secure in 2021? Should I use a different cipher?
Can any metadata leak from the encrypted file?
Should/can the keyfile be larger than 64 bytes?
Should I create new keyfiles for each file I encrypt?
Is there a minimum/maximum file size this can encrypt? Do different file sizes affect security?
Is this considered "rolling my own crypto" (which I know is widely discouraged)?

393

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encryption

aes

openssl

kelalaka

10/12/22, 11:17 AM

Why do you choose CBC instead of AES-GCM or ChaCha20-Poly1305. Encrypted data only contains IV nothin more since AES is secure. Well, why don't you use a VeraCrypy volume to store these files? Also see [this](https://crypto.stackexchange.com/a/87033/18298)

SAI Peregrinus

10/12/22, 12:26 PM

OpenSSL command line only supports less-secure modes like CBC. A VeraCrypt volume would use XTS, which also isn't an AEAD. It's also a lot harder to ensure no nonce reuse with file encryption and a short nonce like GCM uses. XChaCha20-Poly1305 can use a random nonce safely due to its eXtended nonce length.

henderson

10/12/22, 12:44 PM

I need to encrypt files on demand and individually. VeraCrypt does not seem to be able to do that. OpenSSL is not a requirement, it is just the best tool I've found that fits (or at least, seems to fit) my requirements. @SAIPeregrinus

SAI Peregrinus

10/12/22, 4:12 PM

https://age-encryption.org is what I'd recommend. It's built for file encryption, can generate a secure passphrase (eliminating the weak password problem), and uses an actual AEAD unlike OpenSSL, Veracrypt, and GPG. Example use: `age -p -o output.age input.txt` would encrypt `input.txt` into a file `output.txt` and print the passphrase it used. You could also pass in your own passphrase, but I recommend against this. If you want to encrypt lots of files, use its SSH key options.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Is OpenSSL enc using AES-256-CBC to encrypt large files safe?

TH: OpenSSL enc ใช้ AES-256-CBC เพื่อเข้ารหัสไฟล์ขนาดใหญ่ปลอดภัยหรือไม่

RO: Este OpenSSL enc folosind AES-256-CBC pentru a cripta fișierele mari în siguranță?

RU: Безопасно ли OpenSSL enc использует AES-256-CBC для шифрования больших файлов?

VI: OpenSSL enc sử dụng AES-256-CBC để mã hóa các tệp lớn có an toàn không?

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