File nist_kw.h

This file provides an API for key wrapping (KW) and key wrapping with padding (KWP) as defined in NIST SP 800-38F. https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-38F.pdf.

Key wrapping specifies a deterministic authenticated-encryption mode of operation, according to NIST SP 800-38F: Recommendation for Block Cipher Modes of Operation: Methods for Key Wrapping. Its purpose is to protect cryptographic keys.

Its equivalent is RFC 3394 for KW, and RFC 5649 for KWP. https://tools.ietf.org/html/rfc3394 https://tools.ietf.org/html/rfc5649

Enums

enum mbedtls_nist_kw_mode_t

Values:

enumerator MBEDTLS_KW_MODE_KW
enumerator MBEDTLS_KW_MODE_KWP

Functions

void mbedtls_nist_kw_init(mbedtls_nist_kw_context *ctx)

This function initializes the specified key wrapping context to make references valid and prepare the context for mbedtls_nist_kw_setkey() or mbedtls_nist_kw_free().

Parameters:

ctx – The key wrapping context to initialize.

int mbedtls_nist_kw_setkey(mbedtls_nist_kw_context *ctx, mbedtls_cipher_id_t cipher, const unsigned char *key, unsigned int keybits, const int is_wrap)

This function initializes the key wrapping context set in the ctx parameter and sets the encryption key.

Parameters:

  • ctx – The key wrapping context.

  • cipher – The 128-bit block cipher to use. Only AES is supported.

  • key – The Key Encryption Key (KEK).

  • keybits – The KEK size in bits. This must be acceptable by the cipher.

  • is_wrap – Specify whether the operation within the context is wrapping or unwrapping

Returns:

0 on success.

Returns:

MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA for any invalid input.

Returns:

MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE for 128-bit block ciphers which are not supported.

Returns:

cipher-specific error code on failure of the underlying cipher.

void mbedtls_nist_kw_free(mbedtls_nist_kw_context *ctx)

This function releases and clears the specified key wrapping context and underlying cipher sub-context.

Parameters:

ctx – The key wrapping context to clear.

int mbedtls_nist_kw_wrap(mbedtls_nist_kw_context *ctx, mbedtls_nist_kw_mode_t mode, const unsigned char *input, size_t in_len, unsigned char *output, size_t *out_len, size_t out_size)

This function encrypts a buffer using key wrapping.

Parameters:

  • ctx – The key wrapping context to use for encryption.

  • mode – The key wrapping mode to use (MBEDTLS_KW_MODE_KW or MBEDTLS_KW_MODE_KWP)

  • input – The buffer holding the input data.

  • in_len – The length of the input data in Bytes. The input uses units of 8 Bytes called semiblocks.

    • For KW mode: a multiple of 8 bytes between 16 and 2^57-8 inclusive.

    • For KWP mode: any length between 1 and 2^32-1 inclusive.

  • output – [out] The buffer holding the output data.

    • For KW mode: Must be at least 8 bytes larger than in_len.

    • For KWP mode: Must be at least 8 bytes larger rounded up to a multiple of 8 bytes for KWP (15 bytes at most).

  • out_len – [out] The number of bytes written to the output buffer. 0 on failure.

  • out_size – [in] The capacity of the output buffer.

Returns:

0 on success.

Returns:

MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA for invalid input length.

Returns:

cipher-specific error code on failure of the underlying cipher.

int mbedtls_nist_kw_unwrap(mbedtls_nist_kw_context *ctx, mbedtls_nist_kw_mode_t mode, const unsigned char *input, size_t in_len, unsigned char *output, size_t *out_len, size_t out_size)

This function decrypts a buffer using key wrapping.

Parameters:

  • ctx – The key wrapping context to use for decryption.

  • mode – The key wrapping mode to use (MBEDTLS_KW_MODE_KW or MBEDTLS_KW_MODE_KWP)

  • input – The buffer holding the input data.

  • in_len – The length of the input data in Bytes. The input uses units of 8 Bytes called semiblocks. The input must be a multiple of semiblocks.

    • For KW mode: a multiple of 8 bytes between 24 and 2^57 inclusive.

    • For KWP mode: a multiple of 8 bytes between 16 and 2^32 inclusive.

  • output – [out] The buffer holding the output data. The output buffer’s minimal length is 8 bytes shorter than in_len.

  • out_len – [out] The number of bytes written to the output buffer. 0 on failure. For KWP mode, the length could be up to 15 bytes shorter than in_len, depending on how much padding was added to the data.

  • out_size – [in] The capacity of the output buffer.

Returns:

0 on success.

Returns:

MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA for invalid input length.

Returns:

MBEDTLS_ERR_CIPHER_AUTH_FAILED for verification failure of the ciphertext.

Returns:

cipher-specific error code on failure of the underlying cipher.

int mbedtls_nist_kw_self_test(int verbose)

The key wrapping checkup routine.

Returns:

0 on success.

Returns:

1 on failure.

struct mbedtls_nist_kw_context
#include <nist_kw.h>

The key wrapping context-type definition. The key wrapping context is passed to the APIs called.

Note

The definition of this type may change in future library versions. Don’t make any assumptions on this context!

Public Members

mbedtls_cipher_context_t private_cipher_ctx

The cipher context used.