This file contains Diffie-Hellman-Merkle (DHM) key exchange definitions and functions. More...

Data Structures
struct	mbedtls_dhm_context
	The DHM context structure. More...
Typedefs
typedef struct mbedtls_dhm_context	mbedtls_dhm_context
	The DHM context structure.
Functions
void	mbedtls_dhm_init (mbedtls_dhm_context *ctx)
	This function initializes the DHM context.
int	mbedtls_dhm_read_params (mbedtls_dhm_context ctx, unsigned char p, const unsigned char end)
	This function parses the DHM parameters in a TLS ServerKeyExchange handshake message (DHM modulus, generator, and public key).
int	mbedtls_dhm_make_params (mbedtls_dhm_context ctx, int x_size, unsigned char output, size_t olen, int(f_rng)(void , unsigned char , size_t), void *p_rng)
	This function generates a DHM key pair and exports its public part together with the DHM parameters in the format used in a TLS ServerKeyExchange handshake message.
int	mbedtls_dhm_set_group (mbedtls_dhm_context ctx, const mbedtls_mpi P, const mbedtls_mpi *G)
	This function sets the prime modulus and generator.
int	mbedtls_dhm_read_public (mbedtls_dhm_context ctx, const unsigned char input, size_t ilen)
	This function imports the raw public value of the peer.
int	mbedtls_dhm_make_public (mbedtls_dhm_context ctx, int x_size, unsigned char output, size_t olen, int(f_rng)(void , unsigned char , size_t), void p_rng)
	This function creates a DHM key pair and exports the raw public key in big-endian format.
int	mbedtls_dhm_calc_secret (mbedtls_dhm_context ctx, unsigned char output, size_t output_size, size_t olen, int(f_rng)(void , unsigned char , size_t), void *p_rng)
	This function derives and exports the shared secret (G^Y)^X mod `P`.
void	mbedtls_dhm_free (mbedtls_dhm_context *ctx)
	This function frees and clears the components of a DHM context.
int	mbedtls_dhm_parse_dhm (mbedtls_dhm_context dhm, const unsigned char dhmin, size_t dhminlen)
	This function parses DHM parameters in PEM or DER format.
int	mbedtls_dhm_parse_dhmfile (mbedtls_dhm_context dhm, const char path)
	This function loads and parses DHM parameters from a file.
int	mbedtls_dhm_self_test (int verbose)
	The DMH checkup routine.

Detailed Description

This file contains Diffie-Hellman-Merkle (DHM) key exchange definitions and functions.

Diffie-Hellman-Merkle (DHM) key exchange is defined in RFC-2631: Diffie-Hellman Key Agreement Method and Public-Key Cryptography Standards (PKCS) #3: Diffie Hellman Key Agreement Standard.

RFC-3526: More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE) defines a number of standardized Diffie-Hellman groups for IKE.

RFC-5114: Additional Diffie-Hellman Groups for Use with IETF Standards defines a number of standardized Diffie-Hellman groups that can be used.

Warning:: The security of the DHM key exchange relies on the proper choice of prime modulus - optimally, it should be a safe prime. The usage of non-safe primes both decreases the difficulty of the underlying discrete logarithm problem and can lead to small subgroup attacks leaking private exponent bits when invalid public keys are used and not detected. This is especially relevant if the same DHM parameters are reused for multiple key exchanges as in static DHM, while the criticality of small-subgroup attacks is lower for ephemeral DHM.; For performance reasons, the code does neither perform primality nor safe primality tests, nor the expensive checks for invalid subgroups. Moreover, even if these were performed, non-standardized primes cannot be trusted because of the possibility of backdoors that can't be effectively checked for.; Diffie-Hellman-Merkle is therefore a security risk when not using standardized primes generated using a trustworthy ("nothing up my sleeve") method, such as the RFC 3526 / 7919 primes. In the TLS protocol, DH parameters need to be negotiated, so using the default primes systematically is not always an option. If possible, use Elliptic Curve Diffie-Hellman (ECDH), which has better performance, and for which the TLS protocol mandates the use of standard parameters.

Definition in file dhm.h.

Typedef Documentation

typedef struct mbedtls_dhm_context mbedtls_dhm_context

The DHM context structure.

Function Documentation

int mbedtls_dhm_calc_secret	(	mbedtls_dhm_context *	ctx,
		unsigned char *	output,
		size_t	output_size,
		size_t *	olen,
		int()(void , unsigned char *, size_t)	f_rng,
		void *	p_rng
	)

This function derives and exports the shared secret (G^Y)^X mod P.

Note:: If f_rng is not NULL, it is used to blind the input as a countermeasure against timing attacks. Blinding is used only if our private key X is re-used, and not used otherwise. We recommend always passing a non-NULL f_rng argument.

Parameters:

ctx	The DHM context to use. This must be initialized and have its own private key generated and the peer's public key imported.
output	The buffer to write the generated shared key to. This must be a writable buffer of size `output_size` Bytes.
output_size	The size of the destination buffer. This must be at least the size of `ctx->len` (the size of `P`).
olen	On exit, holds the actual number of Bytes written.
f_rng	The RNG function, for blinding purposes. This may b `NULL` if blinding isn't needed.
p_rng	The RNG context. This may be `NULL` if `f_rng` doesn't need a context argument.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 394 of file dhm.c.

void mbedtls_dhm_free ( mbedtls_dhm_context * ctx )

This function frees and clears the components of a DHM context.

Parameters:

ctx	The DHM context to free and clear. This may be `NULL`, in which case this function is a no-op. If it is not `NULL`, it must point to an initialized DHM context.

Definition at line 450 of file dhm.c.

void mbedtls_dhm_init ( mbedtls_dhm_context * ctx )

This function initializes the DHM context.

Parameters:

ctx	The DHM context to initialize.

Definition at line 127 of file dhm.c.

int mbedtls_dhm_make_params	(	mbedtls_dhm_context *	ctx,
		int	x_size,
		unsigned char *	output,
		size_t *	olen,
		int()(void , unsigned char *, size_t)	f_rng,
		void *	p_rng
	)

This function generates a DHM key pair and exports its public part together with the DHM parameters in the format used in a TLS ServerKeyExchange handshake message.

Note:: This function assumes that the DHM parameters ctx->P and ctx->G have already been properly set. For that, use mbedtls_dhm_set_group() below in conjunction with mbedtls_mpi_read_binary() and mbedtls_mpi_read_string().; In a TLS handshake, this is the how the server generates and exports its DHM key material.

Parameters:

ctx	The DHM context to use. This must be initialized and have the DHM parameters set. It may or may not already have imported the peer's public key.
x_size	The private key size in Bytes.
olen	The address at which to store the number of Bytes written on success. This must not be `NULL`.
output	The destination buffer. This must be a writable buffer of sufficient size to hold the reduced binary presentation of the modulus, the generator and the public key, each wrapped with a 2-byte length field. It is the responsibility of the caller to ensure that enough space is available. Refer to mbedtls_mpi_size() to computing the byte-size of an MPI.
f_rng	The RNG function. Must not be `NULL`.
p_rng	The RNG context to be passed to `f_rng`. This may be `NULL` if `f_rng` doesn't need a context parameter.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 161 of file dhm.c.

int mbedtls_dhm_make_public	(	mbedtls_dhm_context *	ctx,
		int	x_size,
		unsigned char *	output,
		size_t	olen,
		int()(void , unsigned char *, size_t)	f_rng,
		void *	p_rng
	)

This function creates a DHM key pair and exports the raw public key in big-endian format.

Note:: The destination buffer is always fully written so as to contain a big-endian representation of G^X mod P. If it is larger than ctx->len, it is padded accordingly with zero-bytes at the beginning.

Parameters:

ctx	The DHM context to use. This must be initialized and have the DHM parameters set. It may or may not already have imported the peer's public key.
x_size	The private key size in Bytes.
output	The destination buffer. This must be a writable buffer of size `olen` Bytes.
olen	The length of the destination buffer. This must be at least equal to `ctx->len` (the size of `P`).
f_rng	The RNG function. This must not be `NULL`.
p_rng	The RNG context to be passed to `f_rng`. This may be `NULL` if `f_rng` doesn't need a context argument.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 279 of file dhm.c.

int mbedtls_dhm_parse_dhm	(	mbedtls_dhm_context *	dhm,
		const unsigned char *	dhmin,
		size_t	dhminlen
	)

This function parses DHM parameters in PEM or DER format.

Parameters:

dhm	The DHM context to import the DHM parameters into. This must be initialized.
dhmin	The input buffer. This must be a readable buffer of length `dhminlen` Bytes.
dhminlen	The size of the input buffer `dhmin`, including the terminating `NULL` Byte for PEM data.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX or MBEDTLS_ERR_PEM_XXX error code on failure.

Definition at line 473 of file dhm.c.

int mbedtls_dhm_parse_dhmfile	(	mbedtls_dhm_context *	dhm,
		const char *	path
	)

This function loads and parses DHM parameters from a file.

Parameters:

dhm	The DHM context to load the parameters to. This must be initialized.
path	The filename to read the DHM parameters from. This must not be `NULL`.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX or MBEDTLS_ERR_PEM_XXX error code on failure.

Definition at line 628 of file dhm.c.

int mbedtls_dhm_read_params	(	mbedtls_dhm_context *	ctx,
		unsigned char **	p,
		const unsigned char *	end
	)

This function parses the DHM parameters in a TLS ServerKeyExchange handshake message (DHM modulus, generator, and public key).

Note:: In a TLS handshake, this is the how the client sets up its DHM context from the server's public DHM key material.

Parameters:

ctx	The DHM context to use. This must be initialized.
p	On input, p must be the start of the input buffer. On output, p is updated to point to the end of the data that has been read. On success, this is the first byte past the end of the ServerKeyExchange parameters. On error, this is the point at which an error has been detected, which is usually not useful except to debug failures.
end	The end of the input buffer.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 136 of file dhm.c.

int mbedtls_dhm_read_public	(	mbedtls_dhm_context *	ctx,
		const unsigned char *	input,
		size_t	ilen
	)

This function imports the raw public value of the peer.

Note:: In a TLS handshake, this is the how the server imports the Client's public DHM key.

Parameters:

ctx	The DHM context to use. This must be initialized and have its DHM parameters set, e.g. via mbedtls_dhm_set_group(). It may or may not already have generated its own private key.
input	The input buffer containing the `G^Y` value of the peer. This must be a readable buffer of size `ilen` Bytes.
ilen	The size of the input buffer `input` in Bytes.

Returns:: 0 on success.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 260 of file dhm.c.

int mbedtls_dhm_self_test ( int verbose )

The DMH checkup routine.

Returns:: 0 on success.; 1 on failure.

Definition at line 680 of file dhm.c.

int mbedtls_dhm_set_group	(	mbedtls_dhm_context *	ctx,
		const mbedtls_mpi *	P,
		const mbedtls_mpi *	G
	)

This function sets the prime modulus and generator.

Note:: This function can be used to set ctx->P, ctx->G in preparation for mbedtls_dhm_make_params().

Parameters:

ctx	The DHM context to configure. This must be initialized.
P	The MPI holding the DHM prime modulus. This must be an initialized MPI.
G	The MPI holding the DHM generator. This must be an initialized MPI.

Returns:: 0 if successful.; An MBEDTLS_ERR_DHM_XXX error code on failure.

Definition at line 238 of file dhm.c.

Type:	Library
Created:	17 Dec 2019
Imports:	79
Forks:	0
Commits:	2
Dependents:	2
Dependencies:	0
Followers:	1

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