Asymmetric Cipher Algorithm Definitions — The Linux Kernel 5.18.5-gnu-1 documentation

# Asymmetric Cipher Algorithm Definitions

struct akcipher_request

  public key request

Definition

    struct akcipher_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 For verify op this is signature + digest, in that case total size of src is src_len + dst_len.

`dst`

  Destination data (Should be NULL for verify op)

`src_len`

  Size of the input buffer For verify op it’s size of signature part of src, this part is supposed to be operated by cipher.

`dst_len`

  Size of dst buffer (for all ops except verify). 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. For verify op this is size of digest part in src.

`__ctx`

  Start of private context data

struct akcipher_alg

  generic public key algorithm

Definition

    struct akcipher_alg {
      int (*sign)(struct akcipher_request *req);
      int (*verify)(struct akcipher_request *req);
      int (*encrypt)(struct akcipher_request *req);
      int (*decrypt)(struct akcipher_request *req);
      int (*set_pub_key)(struct crypto_akcipher *tfm, const void *key, unsigned int keylen);
      int (*set_priv_key)(struct crypto_akcipher *tfm, const void *key, unsigned int keylen);
      unsigned int (*max_size)(struct crypto_akcipher *tfm);
      int (*init)(struct crypto_akcipher *tfm);
      void (*exit)(struct crypto_akcipher *tfm);
      unsigned int reqsize;
      struct crypto_alg base;
    };

Members

`sign`

  Function performs a sign operation as defined by public key algorithm. In case of error, where the dst_len was insufficient, the req->dst_len will be updated to the size required for the operation

`verify`

  Function performs a complete verify operation as defined by public key algorithm, returning verification status. Requires digest value as input parameter.

`encrypt`

  Function performs an encrypt operation as defined by public key algorithm. In case of error, where the dst_len was insufficient, the req->dst_len will be updated to the size required for the operation

`decrypt`

  Function performs a decrypt operation as defined by public key algorithm. In case of error, where the dst_len was insufficient, the req->dst_len will be updated to the size required for the operation

`set_pub_key`

  Function invokes the algorithm specific set public key function, which knows how to decode and interpret the BER encoded public key and parameters

`set_priv_key`

  Function invokes the algorithm specific set private key function, which knows how to decode and interpret the BER encoded private key and parameters

`max_size`

  Function returns dest buffer size required for a given key.

`init`

  Initialize the cryptographic transformation object. This function is used to initialize the cryptographic transformation object. This function is called only once at the instantiation time, right after the transformation context was allocated. In case the cryptographic hardware has some special requirements which need to be handled by software, this function shall check for the precise requirement of the transformation and put any software fallbacks in place.

`exit`

  Deinitialize the cryptographic transformation object. This is a counterpart to init, used to remove various changes set in init.

`reqsize`

  Request context size required by algorithm implementation

`base`

  Common crypto API algorithm data structure

# Asymmetric Cipher API

The Public Key API is used with the algorithms of type CRYPTO_ALG_TYPE_AKCIPHER (listed as type “akcipher” in /proc/crypto)

struct crypto_akcipher *crypto_alloc_akcipher(const char *alg_name, u32 type, u32 mask)

  allocate AKCIPHER tfm handle

Parameters

`const char *alg_name`

  is the cra_name / name or cra_driver_name / driver name of the public key algorithm e.g. “rsa”

`u32 type`

  specifies the type of the algorithm

`u32 mask`

  specifies the mask for the algorithm

Description

Allocate a handle for public key algorithm. The returned struct crypto_akcipher is the handle that is required for any subsequent API invocation for the public key operations.

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_akcipher(struct crypto_akcipher *tfm)

  free AKCIPHER tfm handle

Parameters

`struct crypto_akcipher *tfm`

  AKCIPHER tfm handle allocated with `crypto_alloc_akcipher()`

Description

If tfm is a NULL or error pointer, this function does nothing.

unsigned int crypto_akcipher_maxsize(struct crypto_akcipher *tfm)

  Get len for output buffer

Parameters

`struct crypto_akcipher *tfm`

  AKCIPHER tfm handle allocated with `crypto_alloc_akcipher()`

Description

Function returns the dest 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.

int crypto_akcipher_encrypt(struct akcipher_request *req)

  Invoke public key encrypt operation

Parameters

`struct akcipher_request *req`

  asymmetric key request

Description

Function invokes the specific public key encrypt operation for a given public key algorithm

Return

zero on success; error code in case of error

int crypto_akcipher_decrypt(struct akcipher_request *req)

  Invoke public key decrypt operation

Parameters

`struct akcipher_request *req`

  asymmetric key request

Description

Function invokes the specific public key decrypt operation for a given public key algorithm

Return

zero on success; error code in case of error

int crypto_akcipher_sign(struct akcipher_request *req)

  Invoke public key sign operation

Parameters

`struct akcipher_request *req`

  asymmetric key request

Description

Function invokes the specific public key sign operation for a given public key algorithm

Return

zero on success; error code in case of error

int crypto_akcipher_verify(struct akcipher_request *req)

  Invoke public key signature verification

Parameters

`struct akcipher_request *req`

  asymmetric key request

Description

Function invokes the specific public key signature verification operation for a given public key algorithm.

Note

req->dst should be NULL, req->src should point to SG of size (req->src_size + req->dst_size), containing signature (of req->src_size length) with appended digest (of req->dst_size length).

Return

zero on verification success; error code in case of error.

int crypto_akcipher_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)

  Invoke set public key operation

Parameters

`struct crypto_akcipher *tfm`

  tfm handle

`const void *key`

  BER encoded public key, algo OID, paramlen, BER encoded parameters

`unsigned int keylen`

  length of the key (not including other data)

Description

Function invokes the algorithm specific set key function, which knows how to decode and interpret the encoded key and parameters

Return

zero on success; error code in case of error

int crypto_akcipher_set_priv_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)

  Invoke set private key operation

Parameters

`struct crypto_akcipher *tfm`

  tfm handle

`const void *key`

  BER encoded private key, algo OID, paramlen, BER encoded parameters

`unsigned int keylen`

  length of the key (not including other data)

Description

Function invokes the algorithm specific set key function, which knows how to decode and interpret the encoded key and parameters

Return

zero on success; error code in case of error

# Asymmetric Cipher Request Handle

struct akcipher_request *akcipher_request_alloc(struct crypto_akcipher *tfm, gfp_t gfp)

  allocates public key request

Parameters

`struct crypto_akcipher *tfm`

  AKCIPHER tfm handle allocated with `crypto_alloc_akcipher()`

`gfp_t gfp`

  allocation flags

Return

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

void akcipher_request_free(struct akcipher_request *req)

  zeroize and free public key request

Parameters

`struct akcipher_request *req`

  request to free

void akcipher_request_set_callback(struct akcipher_request *req, u32 flgs, crypto_completion_t cmpl, void *data)

  Sets an asynchronous callback.

Parameters

`struct akcipher_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 akcipher_request_set_crypt(struct akcipher_request *req, struct scatterlist *src, struct scatterlist *dst, unsigned int src_len, unsigned int dst_len)

  Sets request parameters

Parameters

`struct akcipher_request *req`

  public key request

`struct scatterlist *src`

  ptr to input scatter list

`struct scatterlist *dst`

  ptr to output scatter list or NULL for verify op

`unsigned int src_len`

  size of the src input scatter list to be processed

`unsigned int dst_len`

  size of the dst output scatter list or size of signature portion in src for verify op

Description

Sets parameters required by crypto operation