• Mar 14, 2018  There are a number of methods for generating a symmetric key but we’ll focus specifically here on two methods: Direct Key Generation – A key generation algorithm is invoked that uses random bits coming from a PRNG as input. Typically, an application that is encrypting data would use direct key generation as part of its encryption processes. Below is an example of how an AES-128 symmetric key.
• AES encryption uses a single key as a part of the encryption process. The key can be 128 bits (16 bytes), 192 bits (24 bytes), or 256 bits (32 bytes) in length. Given that the fastest computer would take billions of years to run through every permutation of a 256-bit key, AES is considered an extremely secure encryption standard.
• I am currently working on a file encryption software that works via AES-GCM-256 and I am looking for feedback on the encryption key generation process I intend to implement. So far, I have come up with the following process: User supplies password or key file. Then, per file that is to be encrypted.
• If you want to manually specify the provider, just call KeyGenerator.getInstance('AES', 'providerName'). For a truly secure key, you need to be using a hardware security module (HSM) to generate and protect the key. HSM manufacturers will typically supply a JCE provider that will do all the key generation for you, using the code above.
• . AES allows for three different key lengths: 128, 192, or 256 bits. Most of our discussion will assume that the key length is 128 bits. With regard to using a key length other than 128 bits, the main thing that changes in AES is how you generate the key schedule from the key — an issue I address at the end of Section 8.8.1.

1. Process Of Key Generation In Aesthetic
2. Aes Key Iv
3. Aes Key Generator

The 'key expansion' or subkey generation in AES is an iterative process. Due to some work I am doing about this block cipher I have prepared an figure that may help you: The algorithm is checking if the iterator of the generator is in congruent with 0 modulo #columns to proceed with 3 operations or only with one if is not.

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The more popular and widely adopted symmetric encryption algorithm likely to be encountered nowadays is the Advanced Encryption Standard (AES). It is found at least six time faster than triple DES.

A replacement for DES was needed as its key size was too small. With increasing computing power, it was considered vulnerable against exhaustive key search attack. Triple DES was designed to overcome this drawback but it was found slow.

The features of AES are as follows −

• Symmetric key symmetric block cipher
• 128-bit data, 128/192/256-bit keys
• Stronger and faster than Triple-DES
• Provide full specification and design details
• Software implementable in C and Java

Operation of AES

AES is an iterative rather than Feistel cipher. It is based on ‘substitution–permutation network’. It comprises of a series of linked operations, some of which involve replacing inputs by specific outputs (substitutions) and others involve shuffling bits around (permutations).

Interestingly, AES performs all its computations on bytes rather than bits. Hence, AES treats the 128 bits of a plaintext block as 16 bytes. These 16 bytes are arranged in four columns and four rows for processing as a matrix −

Unlike DES, the number of rounds in AES is variable and depends on the length of the key. AES uses 10 rounds for 128-bit keys, 12 rounds for 192-bit keys and 14 rounds for 256-bit keys. Each of these rounds uses a different 128-bit round key, which is calculated from the original AES key.

The schematic of AES structure is given in the following illustration −

Encryption Process

Here, we restrict to description of a typical round of AES encryption. Each round comprise of four sub-processes. The first round process is depicted below −

Byte Substitution (SubBytes)

The 16 input bytes are substituted by looking up a fixed table (S-box) given in design. The result is in a matrix of four rows and four columns.

Shiftrows

Each of the four rows of the matrix is shifted to the left. Any entries that ‘fall off’ are re-inserted on the right side of row. Shift is carried out as follows −

• First row is not shifted.

• Second row is shifted one (byte) position to the left.

• Third row is shifted two positions to the left.

• Fourth row is shifted three positions to the left.

• The result is a new matrix consisting of the same 16 bytes but shifted with respect to each other.

MixColumns

Each column of four bytes is now transformed using a special mathematical function. This function takes as input the four bytes of one column and outputs four completely new bytes, which replace the original column. The result is another new matrix consisting of 16 new bytes. It should be noted that this step is not performed in the last round.

Addroundkey

The 16 bytes of the matrix are now considered as 128 bits and are XORed to the 128 bits of the round key. If this is the last round then the output is the ciphertext. Otherwise, the resulting 128 bits are interpreted as 16 bytes and we begin another similar round.

Decryption Process

The process of decryption of an AES ciphertext is similar to the encryption process in the reverse order. Each round consists of the four processes conducted in the reverse order −

• Add round key
• Mix columns
• Shift rows
• Byte substitution

Since sub-processes in each round are in reverse manner, unlike for a Feistel Cipher, the encryption and decryption algorithms needs to be separately implemented, although they are very closely related.

AES Analysis

In present day cryptography, AES is widely adopted and supported in both hardware and software. Till date, no practical cryptanalytic attacks against AES has been discovered. Additionally, AES has built-in flexibility of key length, which allows a degree of ‘future-proofing’ against progress in the ability to perform exhaustive key searches.

However, just as for DES, the AES security is assured only if it is correctly implemented and good key management is employed.

Introduction

Recently we had a requirement in our organization to implement encryption for all data transmission happening from SAP to external systems to have an additional layer of security. The requirement was to AES256 encrypt and Base64 Encode the information shared between the systems.The encryption/decryption was done with a common key which gets generated in SAP and shared through automated email from the system.

SAP Class/Function Modules used for the process:

• CL_SEC_SXML_WRITER is used to implement the logic for generation of AES key and encryption/decryption of information.
• SCMS_BASE64_<EN/DE>CODE_STR FM is being used for Base64 Encoding/Decoding the information.

High Level Process Flow

Following are the steps and sample code we have used for encryption/decryption.

Generate Encryption Key

We use following logic to generate Key for encryption which is stored in a table and then shared with external systems.

Decryption

Process Of Key Generation In Aesthetic

External System sends AES encrypted and Base64 encoded data and in SAP we used following logic to decrypt the text.

Encryption:

SAP processes the information and sends encrypted response back using following logic:

Sample Output:

Conclusion

Aes Key Iv

The blog post provides information on how to encrypt and decrypt information in SAP and how you can plan the integration with external systems. The sample code here works for AES256/CBC/PKCS5 Padding algorithm, but CL_SEC_SXML_WRITER class has other AES encryption algorithms as well.

Please note along with the encryption key, we also need to share the IV key which is 16bit hexadecimal string (‘0000000000000000’).

Aes Key Generator

Hopefully this blog post will help in implementing similar requirements where we need to send encrypted information between multiple systems.