Key-agreement Protocol Primitives (KPP) Cipher Algorithm Definitions¶

struct kpp_request¶

Definition

struct kpp_request {
  struct crypto_async_request base;
  struct scatterlist * src;
  struct scatterlist * dst;
  unsigned int src_len;
  unsigned int dst_len;
  void * __ctx;
};

Members

base: Common attributes for async crypto requests
src: Source data
dst: Destination data
src_len: Size of the input buffer
dst_len: Size of the output buffer. It needs to be at least as big as the expected result depending on the operation After operation it will be updated with the actual size of the result. In case of error where the dst sgl size was insufficient, it will be updated to the size required for the operation.
__ctx: Start of private context data

struct crypto_kpp¶: user-instantiated object which encapsulate algorithms and core processing logic

Definition

struct crypto_kpp {
  struct crypto_tfm base;
};

Members

base: Common crypto API algorithm data structure

struct kpp_alg¶: generic key-agreement protocol primitives

Definition

struct kpp_alg {
  int (* set_secret) (struct crypto_kpp *tfm, const void *buffer, unsigned int len);
  int (* generate_public_key) (struct kpp_request *req);
  int (* compute_shared_secret) (struct kpp_request *req);
  unsigned int (* max_size) (struct crypto_kpp *tfm);
  int (* init) (struct crypto_kpp *tfm);
  void (* exit) (struct crypto_kpp *tfm);
  unsigned int reqsize;
  struct crypto_alg base;
};

Members

set_secret: Function invokes the protocol specific function to store the secret private key along with parameters. The implementation knows how to decode the buffer
generate_public_key: Function generate the public key to be sent to the counterpart. In case of error, where output is not big enough req->dst_len will be updated to the size required
compute_shared_secret: Function compute the shared secret as defined by the algorithm. The result is given back to the user. In case of error, where output is not big enough, req->dst_len will be updated to the size required
max_size: Function returns the size of the output buffer
init: Initialize the object. This is called only once at instantiation time. In case the cryptographic hardware needs to be initialized. Software fallback should be put in place here.
exit: Undo everything init did.
reqsize: Request context size required by algorithm implementation
base: Common crypto API algorithm data structure

struct kpp_secret¶: small header for packing secret buffer

Definition

struct kpp_secret {
  unsigned short type;
  unsigned short len;
};

Members

type: define type of secret. Each kpp type will define its own
len: specify the len of the secret, include the header, that follows the struct

Key-agreement Protocol Primitives (KPP) Cipher API¶

The KPP API is used with the algorithm type CRYPTO_ALG_TYPE_KPP (listed as type “kpp” in /proc/crypto)

struct crypto_kpp * crypto_alloc_kpp(const char * alg_name, u32 type, u32 mask)¶: allocate KPP tfm handle

Parameters

const char * alg_name: is the name of the kpp algorithm (e.g. “dh”, “ecdh”)
u32 type: specifies the type of the algorithm
u32 mask: specifies the mask for the algorithm

Description

Allocate a handle for kpp algorithm. The returned struct crypto_kpp is required for any following API invocation

Return

allocated handle in case of success; IS_ERR() is true in case of: an error, PTR_ERR() returns the error code.

void crypto_free_kpp(struct crypto_kpp * tfm)¶: free KPP tfm handle

Parameters

struct crypto_kpp * tfm: KPP tfm handle allocated with crypto_alloc_kpp()

int crypto_kpp_set_secret(struct crypto_kpp * tfm, const void * buffer, unsigned int len)¶: Invoke kpp operation

Parameters

struct crypto_kpp * tfm: tfm handle
const void * buffer: Buffer holding the packet representation of the private key. The structure of the packet key depends on the particular KPP implementation. Packing and unpacking helpers are provided for ECDH and DH (see the respective header files for those implementations).
unsigned int len: Length of the packet private key buffer.

Description

Function invokes the specific kpp operation for a given alg.

Return

zero on success; error code in case of error

int crypto_kpp_generate_public_key(struct kpp_request * req)¶: Invoke kpp operation

Parameters

struct kpp_request * req: kpp key request

Description

Function invokes the specific kpp operation for generating the public part for a given kpp algorithm.

To generate a private key, the caller should use a random number generator. The output of the requested length serves as the private key.

Return

zero on success; error code in case of error

int crypto_kpp_compute_shared_secret(struct kpp_request * req)¶: Invoke kpp operation

Parameters

struct kpp_request * req: kpp key request

Description

Function invokes the specific kpp operation for computing the shared secret for a given kpp algorithm.

Return

zero on success; error code in case of error

unsigned int crypto_kpp_maxsize(struct crypto_kpp * tfm)¶: Get len for output buffer

Parameters

struct crypto_kpp * tfm: KPP tfm handle allocated with crypto_alloc_kpp()

Description

Function returns the output buffer size required for a given key. Function assumes that the key is already set in the transformation. If this function is called without a setkey or with a failed setkey, you will end up in a NULL dereference.

Key-agreement Protocol Primitives (KPP) Cipher Request Handle¶

struct kpp_request * kpp_request_alloc(struct crypto_kpp * tfm, gfp_t gfp)¶: allocates kpp request

Parameters

struct crypto_kpp * tfm: KPP tfm handle allocated with crypto_alloc_kpp()
gfp_t gfp: allocation flags

Return

allocated handle in case of success or NULL in case of an error.

void kpp_request_free(struct kpp_request * req)¶: zeroize and free kpp request

Parameters

struct kpp_request * req: request to free

void kpp_request_set_callback(struct kpp_request * req, u32 flgs, crypto_completion_t cmpl, void * data)¶: Sets an asynchronous callback.

Parameters

struct kpp_request * req: request that the callback will be set for
u32 flgs: specify for instance if the operation may backlog
crypto_completion_t cmpl: callback which will be called
void * data: private data used by the caller

Description

Callback will be called when an asynchronous operation on a given request is finished.

void kpp_request_set_input(struct kpp_request * req, struct scatterlist * input, unsigned int input_len)¶: Sets input buffer

Parameters

struct kpp_request * req: kpp request
struct scatterlist * input: ptr to input scatter list
unsigned int input_len: size of the input scatter list

Description

Sets parameters required by generate_public_key

void kpp_request_set_output(struct kpp_request * req, struct scatterlist * output, unsigned int output_len)¶: Sets output buffer

Parameters

struct kpp_request * req: kpp request
struct scatterlist * output: ptr to output scatter list
unsigned int output_len: size of the output scatter list

Description

Sets parameters required by kpp operation

ECDH Helper Functions¶

To use ECDH with the KPP cipher API, the following data structure and functions should be used.

The ECC curves known to the ECDH implementation are specified in this header file.

To use ECDH with KPP, the following functions should be used to operate on an ECDH private key. The packet private key that can be set with the KPP API function call of crypto_kpp_set_secret.

struct ecdh¶: define an ECDH private key

Definition

struct ecdh {
  unsigned short curve_id;
  char * key;
  unsigned short key_size;
};

Members

curve_id: ECC curve the key is based on.
key: Private ECDH key
key_size: Size of the private ECDH key

int crypto_ecdh_key_len(const struct ecdh * params)¶: Obtain the size of the private ECDH key

Parameters

const struct ecdh * params: private ECDH key

Description

This function returns the packet ECDH key size. A caller can use that with the provided ECDH private key reference to obtain the required memory size to hold a packet key.

Return

size of the key in bytes

int crypto_ecdh_encode_key(char * buf, unsigned int len, const struct ecdh * p)¶: encode the private key

Parameters

char * buf: Buffer allocated by the caller to hold the packet ECDH private key. The buffer should be at least crypto_ecdh_key_len bytes in size.
unsigned int len: Length of the packet private key buffer
const struct ecdh * p: Buffer with the caller-specified private key

Description

The ECDH implementations operate on a packet representation of the private key.

Return

-EINVAL if buffer has insufficient size, 0 on success

int crypto_ecdh_decode_key(const char * buf, unsigned int len, struct ecdh * p)¶: decode a private key

Parameters

const char * buf: Buffer holding a packet key that should be decoded
unsigned int len: Length of the packet private key buffer
struct ecdh * p: Buffer allocated by the caller that is filled with the unpacked ECDH private key.

Description

The unpacking obtains the private key by pointing p to the correct location in buf. Thus, both pointers refer to the same memory.

Return

-EINVAL if buffer has insufficient size, 0 on success

DH Helper Functions¶

To use DH with the KPP cipher API, the following data structure and functions should be used.

To use DH with KPP, the following functions should be used to operate on a DH private key. The packet private key that can be set with the KPP API function call of crypto_kpp_set_secret.

struct dh¶: define a DH private key

Definition

struct dh {
  void * key;
  void * p;
  void * g;
  unsigned int key_size;
  unsigned int p_size;
  unsigned int g_size;
};

Members

key: Private DH key
p: Diffie-Hellman parameter P
g: Diffie-Hellman generator G
key_size: Size of the private DH key
p_size: Size of DH parameter P
g_size: Size of DH generator G

int crypto_dh_key_len(const struct dh * params)¶: Obtain the size of the private DH key

Parameters

const struct dh * params: private DH key

Description

This function returns the packet DH key size. A caller can use that with the provided DH private key reference to obtain the required memory size to hold a packet key.

Return

size of the key in bytes

int crypto_dh_encode_key(char * buf, unsigned int len, const struct dh * params)¶: encode the private key

Parameters

char * buf: Buffer allocated by the caller to hold the packet DH private key. The buffer should be at least crypto_dh_key_len bytes in size.
unsigned int len: Length of the packet private key buffer
const struct dh * params: Buffer with the caller-specified private key

Description

The DH implementations operate on a packet representation of the private key.

Return

-EINVAL if buffer has insufficient size, 0 on success

int crypto_dh_decode_key(const char * buf, unsigned int len, struct dh * params)¶: decode a private key

Parameters

const char * buf: Buffer holding a packet key that should be decoded
unsigned int len: Length of the packet private key buffer
struct dh * params: Buffer allocated by the caller that is filled with the unpacked DH private key.

Description

The unpacking obtains the private key by pointing p to the correct location in buf. Thus, both pointers refer to the same memory.

Return

-EINVAL if buffer has insufficient size, 0 on success