Information Security
Baskoro Adi Pratomo
Informatics Department
Institut Teknologi Sepuluh Nopember
Surabaya, Indonesia
2021
Encryption algorithm usage
• Which algorithm should we use for the following
cases?
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Encrypting AES key
Encrypting password
Encrypting searchable content (e.g., address or name)
Encrypting a PDF document
Encrypting chat messages
Best Practice in
Cryptography and Key
Management
Source:
https://cheatsheetseries.owasp.org/cheatsheets/Key_M
anagement_Cheat_Sheet.html
https://cheatsheetseries.owasp.org/cheatsheets/Crypto
graphic_Storage_Cheat_Sheet.html
Where to perform encryption
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At the application level.
At the database level (e.g, SQL Server TDE)
At the filesystem level (e.g, BitLocker or LUKS)
At the hardware level (e.g, encrypted RAID cards or
SSDs)
Which algorithm to use?
• Symmetric
• AES-128 (min) or AES-256 (recommended)
• Asymmetric
• Curve 25519
• RSA (min 2048 bits)
Which algorithm to use?
• Other factors to consider:
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Key size.
Known attacks and weaknesses of the algorithm.
Maturity of the algorithm.
Approval by third parties such as NIST's algorithmic
validation program.
• Performance (both for encryption and decryption).
• Quality of the libraries available.
• Portability of the algorithm (i.e, how widely supported is
it).
Avalanche Effect
• Avalanche Effect:
• A tiny change in the plaintext causes a massive difference
in the ciphertext
This Photo by Unknown Author is licensed under
CC BY-SA
Using custom algorithms?
• DON’T DO THIS
Which mode of operation to use?
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GCM (Galois Counter Mode)
CCM
CTR
CBC
Which random number generator to use?
Key Generation
• Do:
• Generated using a cryptographically secure function
• Don’t:
• Based on common words/phrases
• Generated by mashing the keyboards
Lifetime and Key Rotation
(When to replace a key)
• If the previous key is known (or suspected) to have been
compromised.
• This could also be caused by someone who had access to the
key leaving the organisation.
• After a specified period has elapsed. (See section 5.3 of
NIST SP 800-57 for further guidance.)
• After the key has been used to encrypt a specific amount
of data.
• This would typically be 2^35 bytes (~34GB) for 64-bit keys and
2^68 bytes (~295 exabytes) for 128-bit block size.
• If there is a significant change to the security provided
by the algorithm
• such as a new attack being announced
Lifetime and Key Rotation
(Handling old encrypted data)
• (Preferred) Decrypting it and re-encrypting it with
the new key.
• Marking each item with the ID of the key that was
used to encrypt it, and storing multiple keys to allow
the old data to be decrypted.
Key Storage
• Ideally, we store keys in:
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A physical Hardware Security Module (HSM).
A virtual HSM.
Key vaults such as Amazon KMS or Azure Key Vault.
An external secrets management service such as Conjur
or HashiCorp Vault.
• Secure storage APIs provided by the ProtectedData class
in the .NET framework.
But, life is never ideal
• Requirements for alternative key storage:
• Central management of keys, especially in containerised
environments.
• Easy key rotation and replacement.
• Secure key generation.
• Simplifying compliance with regulatory standards such as
FIPS 140 or PCI DSS.
• Making it harder for an attacker to export or steal keys.
Four sins of key storage
• Hard-coding keys into the application source code.
• Checking keys into version control systems.
• Not protecting the configuration files containing the
keys with restrictive permissions.
• Storing keys in environment variables
• Keys can be accidentally exposed through functions such
as phpinfo() or through the /proc/self/environ file.
Assignment 2: Key Management
• Continuing from the previous assignment, add the
following features to your web app:
• A user can request to see the private data of other users
(including the images and documents)
• The requested user generates a symmetric key to share
the data to the requesting user
• The symmetric key will be distributed to the requesting
user by other means (e.g., email, WA, etc), but it needs to
be encrypted by using asymmetric encryption
• The symmetric keys must be stored securely in the
system