PadLock AES Core test module (1)

First, brief

A verification module for testing the padlock AES kernel interface is written. encrypted decryption is implemented using the PadLock AES kernel interface. This paper provides the method, procedure, principle and source code for applying the module.

Second, the operating environment

Operating system	mint17
Kernel	3.8.0
Compiler	gcc4.7.3
Cpu	VIA Nano X2 L4530 @ 1.6+ GHz
Memory	4G
Multi-core	2 x

Three, the main principle

The Linux kernel has interfaces for cryptographic functions, primarily in the cryto folder directory. There are many algorithms such as AES,SHA , etc. to implement the interface. There are many articles on the web that introduce the Linux kernel's framework of cryptographic algorithms, and by reading the Linux kernel source code, you write an AES Kernel module of the core function library.

There are 4 main functions using the AES encryption Algorithm :

Crypto_blkcipher_setkeycrypto_blkcipher_set_ivcrypto_blkcipher_encryptcrypto_blkcipher_decrypt

Only these functions are properly configured, so you can use the AES Encryption Library of the Linux kernel properly . The usage of these functions is described below.

static inline int Crypto_blkcipher_setkey (struct crypto_blkcipher *tfm,

Const U8 *key, unsigned int keylen)

This function is primarily used to set the encryption keywordKey. Here you need to explain theAESHow to apply the algorithm, for the algorithm level,AESthroughKey (Key Words),IV (initialization Vector), encryption Mode (CBC/ECB/CFB/OFB, etc.),key-length (128/192/256)to determine the mode of encryption, according to different modes of the same plaintext encryption of ciphertext is not the same. Crypto_blkcipher_setkey ()function is to set itsKey. *keyis the secret key,Keylenis the secret key length (unit bytes can be selected -, -, +)

Here is the Crypto_blkcipher *tfm, struct This is the encryption context, it is always through the encryption,Crypto_blkcipher_setkey,crypto_ Blkcipher_set_iv are used to set the structure of TFM, which is the carrier of the encryption configuration.

struct Crypto_blkcipher {struct CRYPTO_TFM base;}; struct CRYPTO_TFM {u32 crt_flags;union {struct ABLKCIPHER_TFM ablkcipher;struct aead_tfm aead;struct blkcipher_tfm blkci Pher;struct cipher_tfm cipher;struct hash_tfm hash;struct compress_tfm compress;struct RNG_TFM rng; Crt_u;   Determine the algorithm pattern void (*exit) (struct CRYPTO_TFM *tfm); Exit Function struct Crypto_alg *__crt_alg;void *__crt_ctx[] crypto_minalign_attr;};

From the middle one.Unionand a bunch of them up there.#defineit can be seen from this structure can be scattered out of a groupXXX_TFM. Crypto_algcorrespondingCIPHER_TFM. The last parameter__crt_ctx[]is the algorithm context mentioned above. In other words, the algorithm context is followedTFMassigned together. FromTFM, we can getCTX. Linuxprovides a functioninline void *crypto_tfm_ctx (struct CRYPTO_TFM *tfm);to perform the conversion, the function is also<srcdir>/include/linux/crypto.hthe.

The crypto_blkcipher_set_iv function is described below

static inline void Crypto_blkcipher_set_iv (struct crypto_blkcipher *tfm,

Const U8 *SRC, unsigned int len)

Its function is to set IV(initialization vector). src is the IV value,len is the length of IV,TFM is the same as the one described earlier.

The following describes the core cryptographic function Crypto_blkcipher_encrypt_iv:

static inline int crypto_blkcipher_encrypt (struct blkcipher_desc *desc,      struct scatterlist *dst,      struct Scatterlist *src,      unsigned int nbytes)

Its function is to implement encryption. Return 0 is correct and1 indicates an error. *desc is a cryptographic context structure, above Set_iv and set_key is used to set this Blkcipher_desc structure of the body,

The prototypes are:

struct Blkcipher_desc {struct crypto_blkcipher *tfm;void *info;u32 flags;};

where TFM is what we call the encryption context,info is typically used to store IV, because the block-encrypted hash sequence tool ( Scatterwalk) uses info as an IV directly at initialization time .

What is a hash sequence (scatterlist)? "1"

InLinuxin the kernel, there are three ways of dealing with peripherals:IO, ports, andDMA, this textbook is all about. WhichDMAWay is byDMAcontroller to control the data transfer between memory and peripherals. We know thatLinuxThere are three types of address space: virtual address, Physical address, and bus address. DMAa whole chunk of data is required to be distributed over a continuous bus address space for each transmission. andDMAis designed for transmitting large chunks of data, but large chunks of contiguous bus address space are often scarce. So when there is not that much contiguous space, you can only spread large chunks of data to as few small contiguous addresses as possible, and then letDMAthe controller passes all the data in one piece. SoLinuxThe kernel is designed specifically for a sequence called a hash set (scatterlist), the data structure of the small block of continuous bus address string up, giveDMAThe drive transmits automatically one after the other.

Plainly,scatterlist is a linear table (scatterlist can be a list or an array), each element contains a pointer to a contiguous block of memory for a bus address, which is DMA -tailored data structure.

Scatterlist structure struct Scatterlist {#ifdef config_debug_sgunsigned longsg_magic;     #endifunsigned Longpage_link;     which page unsigned intoffset;            The offset of the page unsigned intlength;           The length of the data is dma_addr_tdma_address; #ifdef config_need_sg_dma_lengthunsigned intdma_length; #endif};

Allocate space for Scatterwalk and set data utilization function in this article:

Sg_init_one().

Scatterwalk is the operation of physical memory, which facilitates the transmission of DMA. But much of what we do in the Linux kernel is the processing of virtual memory (which shows the data PRINTK), so we also need to apply Scatterwalk and it needs to be mapped to virtual memory to take advantage ( Kmap ), which is described in the following implementation program.

DST is the destination address,src is the original data,nbytes is the byte processed.

The prototype of the Crypto_blkcipher_decrypt function is: static inline int crypto_blkcipher_decrypt (struct blkcipher_desc *desc,   struct Scatterlist *dst,   struct scatterlist *src,   unsigned int nbytes)

This function is decrypted, similar to cryptographic algorithm parameters, and is no longer described.

PadLock AES Core test module (1)