EVP_KDF_SS.7ssl - Man Page

The Single Step / One Step EVP_KDF implementation

Description

The EVP_KDF_SS algorithm implements the Single Step key derivation function (SSKDF). SSKDF derives a key using input such as a shared secret key (that was generated during the execution of a key establishment scheme) and fixedinfo. SSKDF is also informally referred to as 'Concat KDF'.

Auxilary function

The implementation uses a selectable auxiliary function H, which can be in the backported version only a:

H(x) = hash(x, digest=md)

Numeric identity

EVP_KDF_SS is the numeric identity for this implementation; it can be used with the EVP_KDF_CTX_new_id() function.

Supported controls

The supported controls are:

EVP_KDF_CTRL_SET_MD

This control works as described in “CONTROLS” in EVP_KDF_CTX(3).

EVP_KDF_CTRL_SET_KEY

This control expects two arguments: unsigned char *secret, size_t secretlen

The shared secret used for key derivation.  This control sets the secret.

EVP_KDF_ctrl_str() takes two type strings for this control:

“secret”

The value string is used as is.

“hexsecret”

The value string is expected to be a hexadecimal number, which will be decoded before being passed on as the control value.

EVP_KDF_CTRL_SET_SSKDF_INFO

This control expects two arguments: unsigned char *info, size_t infolen

An optional value for fixedinfo, also known as otherinfo. This control sets the fixedinfo.

EVP_KDF_ctrl_str() takes two type strings for this control:

“info”

The value string is used as is.

“hexinfo”

The value string is expected to be a hexadecimal number, which will be decoded before being passed on as the control value.

Notes

A context for SSKDF can be obtained by calling:

EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);

The output length of an SSKDF is specified via the keylen parameter to the EVP_KDF_derive(3) function.

Example

This example derives 10 bytes using H(x) = SHA-256, with the secret key “secret” and fixedinfo value “label”:

  EVP_KDF_CTX *kctx;
  unsigned char out[10];

  kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);

  if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
      error("EVP_KDF_CTRL_SET_MD");
  }
  if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
      error("EVP_KDF_CTRL_SET_KEY");
  }
  if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
      error("EVP_KDF_CTRL_SET_SSKDF_INFO");
  }
  if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
      error("EVP_KDF_derive");
  }

  EVP_KDF_CTX_free(kctx);

Conforming to

NIST SP800-56Cr1.

See Also

EVP_KDF_CTX, EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3), EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), “CONTROLS” in EVP_KDF_CTX(3)

History

This functionality was added to OpenSSL 3.0.0.

Info

2021-03-26 1.1.1k OpenSSL