File ecdsa.h

This file contains ECDSA definitions and functions.

The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography. The use of ECDSA for TLS is defined in RFC-4492: Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS).

Defines

MBEDTLS_ECDSA_MAX_SIG_LEN(bits)

Maximum ECDSA signature size for a given curve bit size.

Note

This macro returns a compile-time constant if its argument is one. It may evaluate its argument multiple times.

Parameters

bits – Curve size in bits

Returns

Maximum signature size in bytes

MBEDTLS_ECDSA_MAX_LEN: The maximal size of an ECDSA signature in Bytes.

Typedefs

typedef mbedtls_ecp_keypair mbedtls_ecdsa_context: The ECDSA context structure.

Note

pk_wrap module assumes that “ecdsa_context” is identical to “ecp_keypair” (see for example structure “mbedtls_eckey_info” where ECDSA sign/verify functions are used also for EC key)

Warning

Performing multiple operations concurrently on the same ECDSA context is not supported; objects of this type should not be shared between multiple threads.

typedef struct mbedtls_ecdsa_restart_ver mbedtls_ecdsa_restart_ver_ctx: Internal restart context for ecdsa_verify()

Note

Opaque struct, defined in ecdsa.c

typedef struct mbedtls_ecdsa_restart_sig mbedtls_ecdsa_restart_sig_ctx: Internal restart context for ecdsa_sign()

Note

Opaque struct, defined in ecdsa.c

typedef struct mbedtls_ecdsa_restart_det mbedtls_ecdsa_restart_det_ctx: Internal restart context for ecdsa_sign_det()

Note

Opaque struct, defined in ecdsa.c

Functions

int mbedtls_ecdsa_can_do(mbedtls_ecp_group_id gid)

This function checks whether a given group can be used for ECDSA.

Parameters: gid – The ECP group ID to check.
Returns: 1 if the group can be used, 0 otherwise

int mbedtls_ecdsa_sign(mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s, const mbedtls_mpi *d, const unsigned char *buf, size_t blen, int (*f_rng)(void*, unsigned char*, size_t), void *p_rng)

This function computes the ECDSA signature of a previously-hashed message.

See also

ecp.h

Note

The deterministic version implemented in mbedtls_ecdsa_sign_det_ext() is usually preferred.

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.3, step 5.

Parameters

grp – The context for the elliptic curve to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
r – The MPI context in which to store the first part the signature. This must be initialized.
s – The MPI context in which to store the second part the signature. This must be initialized.
d – The private signing key. This must be initialized.
buf – The content to be signed. This is usually the hash of the original data to be signed. This must be a readable buffer of length blen Bytes. It may be NULL if blen is zero.
blen – The length of buf in Bytes.
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 parameter.

Returns

0 on success.

Returns

An MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code on failure.

int mbedtls_ecdsa_sign_det_ext(mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s, const mbedtls_mpi *d, const unsigned char *buf, size_t blen, mbedtls_md_type_t md_alg, int (*f_rng_blind)(void*, unsigned char*, size_t), void *p_rng_blind)

This function computes the ECDSA signature of a previously-hashed message, deterministic version.

For more information, see RFC-6979: Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA).

See also

ecp.h

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.3, step 5.

Parameters

grp – The context for the elliptic curve to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
r – The MPI context in which to store the first part the signature. This must be initialized.
s – The MPI context in which to store the second part the signature. This must be initialized.
d – The private signing key. This must be initialized and setup, for example through mbedtls_ecp_gen_privkey().
buf – The hashed content to be signed. This must be a readable buffer of length blen Bytes. It may be NULL if blen is zero.
blen – The length of buf in Bytes.
md_alg – The hash algorithm used to hash the original data.
f_rng_blind – The RNG function used for blinding. This must not be NULL.
p_rng_blind – The RNG context to be passed to f_rng_blind. This may be NULL if f_rng_blind doesn’t need a context parameter.

Returns

0 on success.

Returns

An MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code on failure.

int mbedtls_ecdsa_sign_det_restartable(mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s, const mbedtls_mpi *d, const unsigned char *buf, size_t blen, mbedtls_md_type_t md_alg, int (*f_rng_blind)(void*, unsigned char*, size_t), void *p_rng_blind, mbedtls_ecdsa_restart_ctx *rs_ctx)

This function computes the ECDSA signature of a previously-hashed message, in a restartable way.

See also

ecp.h

Note

This function is like mbedtls_ecdsa_sign_det_ext() but it can return early and restart according to the limit set with mbedtls_ecp_set_max_ops() to reduce blocking.

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.3, step 5.

Parameters

grp – The context for the elliptic curve to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
r – The MPI context in which to store the first part the signature. This must be initialized.
s – The MPI context in which to store the second part the signature. This must be initialized.
d – The private signing key. This must be initialized and setup, for example through mbedtls_ecp_gen_privkey().
buf – The hashed content to be signed. This must be a readable buffer of length blen Bytes. It may be NULL if blen is zero.
blen – The length of buf in Bytes.
md_alg – The hash algorithm used to hash the original data.
f_rng_blind – The RNG function used for blinding. This must not be NULL.
p_rng_blind – The RNG context to be passed to f_rng_blind. This may be NULL if f_rng_blind doesn’t need a context parameter.
rs_ctx – The restart context to use. This may be NULL to disable restarting. If it is not NULL, it must point to an initialized restart context.

Returns

0 on success.

Returns

MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see mbedtls_ecp_set_max_ops().

Returns

Another MBEDTLS_ERR_ECP_XXX, MBEDTLS_ERR_MPI_XXX or MBEDTLS_ERR_ASN1_XXX error code on failure.

int mbedtls_ecdsa_verify(mbedtls_ecp_group *grp, const unsigned char *buf, size_t blen, const mbedtls_ecp_point *Q, const mbedtls_mpi *r, const mbedtls_mpi *s)

This function verifies the ECDSA signature of a previously-hashed message.

See also

ecp.h

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.4, step 3.

Parameters

grp – The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
buf – The hashed content that was signed. This must be a readable buffer of length blen Bytes. It may be NULL if blen is zero.
blen – The length of buf in Bytes.
Q – The public key to use for verification. This must be initialized and setup.
r – The first integer of the signature. This must be initialized.
s – The second integer of the signature. This must be initialized.

Returns

0 on success.

Returns

An MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code on failure.

int mbedtls_ecdsa_write_signature(mbedtls_ecdsa_context *ctx, mbedtls_md_type_t md_alg, const unsigned char *hash, size_t hlen, unsigned char *sig, size_t sig_size, size_t *slen, int (*f_rng)(void*, unsigned char*, size_t), void *p_rng)

This function computes the ECDSA signature and writes it to a buffer, serialized as defined in RFC-4492: Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS).

See also

ecp.h

Note

The deterministic version is used if MBEDTLS_ECDSA_DETERMINISTIC is defined. For more information, see RFC-6979: Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA).

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.3, step 5.

Warning

It is not thread-safe to use the same context in multiple threads.

Parameters

ctx – The ECDSA context to use. This must be initialized and have a group and private key bound to it, for example via mbedtls_ecdsa_genkey() or mbedtls_ecdsa_from_keypair().
md_alg – The message digest that was used to hash the message.
hash – The message hash to be signed. This must be a readable buffer of length hlen Bytes.
hlen – The length of the hash hash in Bytes.
sig – The buffer to which to write the signature. This must be a writable buffer of length at least twice as large as the size of the curve used, plus 9. For example, 73 Bytes if a 256-bit curve is used. A buffer length of MBEDTLS_ECDSA_MAX_LEN is always safe.
sig_size – The size of the sig buffer in bytes.
slen – The address at which to store the actual length of the signature written. Must not be NULL.
f_rng – The RNG function. This must not be NULL if MBEDTLS_ECDSA_DETERMINISTIC is unset. Otherwise, it is used only for blinding and may be set to NULL, but doing so is DEPRECATED.
p_rng – The RNG context to be passed to f_rng. This may be NULL if f_rng is NULL or doesn’t use a context.

Returns

0 on success.

Returns

An MBEDTLS_ERR_ECP_XXX, MBEDTLS_ERR_MPI_XXX or MBEDTLS_ERR_ASN1_XXX error code on failure.

int mbedtls_ecdsa_write_signature_restartable(mbedtls_ecdsa_context *ctx, mbedtls_md_type_t md_alg, const unsigned char *hash, size_t hlen, unsigned char *sig, size_t sig_size, size_t *slen, int (*f_rng)(void*, unsigned char*, size_t), void *p_rng, mbedtls_ecdsa_restart_ctx *rs_ctx)

This function computes the ECDSA signature and writes it to a buffer, in a restartable way.

See also

mbedtls_ecdsa_write_signature()

Note

This function is like mbedtls_ecdsa_write_signature() but it can return early and restart according to the limit set with mbedtls_ecp_set_max_ops() to reduce blocking.

Parameters

ctx – The ECDSA context to use. This must be initialized and have a group and private key bound to it, for example via mbedtls_ecdsa_genkey() or mbedtls_ecdsa_from_keypair().
md_alg – The message digest that was used to hash the message.
hash – The message hash to be signed. This must be a readable buffer of length hlen Bytes.
hlen – The length of the hash hash in Bytes.
sig – The buffer to which to write the signature. This must be a writable buffer of length at least twice as large as the size of the curve used, plus 9. For example, 73 Bytes if a 256-bit curve is used. A buffer length of MBEDTLS_ECDSA_MAX_LEN is always safe.
sig_size – The size of the sig buffer in bytes.
slen – The address at which to store the actual length of the signature written. Must not be NULL.
f_rng – The RNG function. This must not be NULL if MBEDTLS_ECDSA_DETERMINISTIC is unset. Otherwise, it is unused and may be set to NULL.
p_rng – The RNG context to be passed to f_rng. This may be NULL if f_rng is NULL or doesn’t use a context.
rs_ctx – The restart context to use. This may be NULL to disable restarting. If it is not NULL, it must point to an initialized restart context.

Returns

0 on success.

Returns

MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see mbedtls_ecp_set_max_ops().

Returns

Another MBEDTLS_ERR_ECP_XXX, MBEDTLS_ERR_MPI_XXX or MBEDTLS_ERR_ASN1_XXX error code on failure.

int mbedtls_ecdsa_read_signature(mbedtls_ecdsa_context *ctx, const unsigned char *hash, size_t hlen, const unsigned char *sig, size_t slen)

This function reads and verifies an ECDSA signature.

See also

ecp.h

Note

If the bitlength of the message hash is larger than the bitlength of the group order, then the hash is truncated as defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography, section 4.1.4, step 3.

Parameters

ctx – The ECDSA context to use. This must be initialized and have a group and public key bound to it.
hash – The message hash that was signed. This must be a readable buffer of length hlen Bytes.
hlen – The size of the hash hash.
sig – The signature to read and verify. This must be a readable buffer of length slen Bytes.
slen – The size of sig in Bytes.

Returns

0 on success.

Returns

MBEDTLS_ERR_ECP_BAD_INPUT_DATA if signature is invalid.

Returns

MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH if there is a valid signature in sig, but its length is less than siglen.

Returns

An MBEDTLS_ERR_ECP_XXX or MBEDTLS_ERR_MPI_XXX error code on failure for any other reason.

int mbedtls_ecdsa_read_signature_restartable(mbedtls_ecdsa_context *ctx, const unsigned char *hash, size_t hlen, const unsigned char *sig, size_t slen, mbedtls_ecdsa_restart_ctx *rs_ctx)

This function reads and verifies an ECDSA signature, in a restartable way.

See also

mbedtls_ecdsa_read_signature()

Note

This function is like mbedtls_ecdsa_read_signature() but it can return early and restart according to the limit set with mbedtls_ecp_set_max_ops() to reduce blocking.

Parameters

ctx – The ECDSA context to use. This must be initialized and have a group and public key bound to it.
hash – The message hash that was signed. This must be a readable buffer of length hlen Bytes.
hlen – The size of the hash hash.
sig – The signature to read and verify. This must be a readable buffer of length slen Bytes.
slen – The size of sig in Bytes.
rs_ctx – The restart context to use. This may be NULL to disable restarting. If it is not NULL, it must point to an initialized restart context.

Returns

0 on success.

Returns

MBEDTLS_ERR_ECP_BAD_INPUT_DATA if signature is invalid.

Returns

MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH if there is a valid signature in sig, but its length is less than siglen.

Returns

MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see mbedtls_ecp_set_max_ops().

Returns

Another MBEDTLS_ERR_ECP_XXX or MBEDTLS_ERR_MPI_XXX error code on failure for any other reason.

int mbedtls_ecdsa_genkey(mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid, int (*f_rng)(void*, unsigned char*, size_t), void *p_rng)

This function generates an ECDSA keypair on the given curve.

See also

ecp.h

Parameters

ctx – The ECDSA context to store the keypair in. This must be initialized.
gid – The elliptic curve to use. One of the various MBEDTLS_ECP_DP_XXX macros depending on configuration.
f_rng – The RNG function to use. 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.

Returns

An MBEDTLS_ERR_ECP_XXX code on failure.

int mbedtls_ecdsa_from_keypair(mbedtls_ecdsa_context *ctx, const mbedtls_ecp_keypair *key)

This function sets up an ECDSA context from an EC key pair.

See also

ecp.h

Parameters

ctx – The ECDSA context to setup. This must be initialized.
key – The EC key to use. This must be initialized and hold a private-public key pair or a public key. In the former case, the ECDSA context may be used for signature creation and verification after this call. In the latter case, it may be used for signature verification.

Returns

0 on success.

Returns

An MBEDTLS_ERR_ECP_XXX code on failure.

void mbedtls_ecdsa_init(mbedtls_ecdsa_context *ctx)

This function initializes an ECDSA context.

Parameters: ctx – The ECDSA context to initialize. This must not be NULL.

void mbedtls_ecdsa_free(mbedtls_ecdsa_context *ctx)

This function frees an ECDSA context.

Parameters: ctx – The ECDSA context to free. This may be NULL, in which case this function does nothing. If it is not NULL, it must be initialized.

void mbedtls_ecdsa_restart_init(mbedtls_ecdsa_restart_ctx *ctx)

Initialize a restart context.

Parameters: ctx – The restart context to initialize. This must not be NULL.

void mbedtls_ecdsa_restart_free(mbedtls_ecdsa_restart_ctx *ctx)

Free the components of a restart context.

Parameters: ctx – The restart context to free. This may be NULL, in which case this function does nothing. If it is not NULL, it must be initialized.

struct mbedtls_ecdsa_restart_ctx

#include <ecdsa.h>

General context for resuming ECDSA operations.

Public Members

mbedtls_ecp_restart_ctx private_ecp: base context for ECP restart and shared administrative info

mbedtls_ecdsa_restart_ver_ctx *private_ver: ecdsa_verify() sub-context

mbedtls_ecdsa_restart_sig_ctx *private_sig: ecdsa_sign() sub-context

mbedtls_ecdsa_restart_det_ctx *private_det: ecdsa_sign_det() sub-context