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205 lines
7.5 KiB
C
205 lines
7.5 KiB
C
/*
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* SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#pragma once
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#include <stdint.h>
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#include <esp_err.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @brief SRP-6a protocol implementation
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*
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* More information on protocol can be found: https://datatracker.ietf.org/doc/html/rfc5054
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*
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* This implementation is used by security2 of wifi_provisioning and local control features.
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* Details on how these protocols use this feature can be found here: https://docs.espressif.com/projects/esp-idf/en/latest/esp32c3/api-reference/provisioning/provisioning.html#security-2-scheme
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*
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* Below is the example usage of the srp6a protocol in protocomm component,
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* which can help understand the APIs better.
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*
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* Variables used:
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*
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* N, g: group parameters (prime and generator)
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* s: salt
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* B, b: server's public and private values
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* A, a: client's public and private values
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* I: user name (aka "identity")
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* P: password
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* v: verifier
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* k: SRP-6 multiplier
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*
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* salt (s) is random of given length, 16 in our case, which along with username and password
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* is used to generate verifier.
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*
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* x = SHA1(s | SHA1(I | ":" | P))
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* v = g^x % N
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*
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* Steps involved (From protocomm component usage):
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* Step1. Client Hello (PhoneApp):
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* a. Generate Key pair:
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* a (cli_privkey) = 256 bit random value,
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* A (cli_pubkey) = g^a.
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* g - generator, N - large safe prime, All arithmetic operations are performed in ring of integers modulo N,
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* thus all occurrences like y^z should be read as y^z modulo N.
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* b. SessionCmd0 (cli_pubkey, username I)
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*
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* Step2. Device(ESP):
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* a. Obtain Salt and verifier stored on ESP
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* Salt s = 256 bit random value,
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* Verifier v = g^× where x = H(s | I | P)
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* b. Generate Key Pair
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* b (dev_privkey) = 256 bit random value
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* B(dev_pubkey) = k*v + g^b where k = H(N, g)
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* c. Shared Key K = H(S) where,
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* S = (A * v^u) ^ b
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* u = H(A, B)
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* d. SessionResp0(dev_pubkey B, dev_random)
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*
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* Step3. Client (PhoneApp)
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* a. shared_key(K) = H(S) where,
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* S = (B - k*v) ^ (a + ux),
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* u = H(A, B),
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* k = H(N, g),
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* V = g^x,
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* x = H(s | I | P).
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* b. Verification token
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* client proof M = H[H(N) XOR H(g) | H(I) | S | A | B | K]
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* c. SessionCmd1(Client proof M1)
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*
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* Step4. Device (ESP):
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* a. Verify client:
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* device generates M1 = H[H(N) XOR H(g) | H(I) | S | A | B | K]
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* device verifies this M1 with the M1 obtained from Client
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* b. Verification token: Device generate device proof M2 = H(A, M, K)
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* c. Initialization Vector(IV):
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* dev_rand = gen_16byte_random) This random number is to be used for AES-GCM operation
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* for encryption and decryption of the data using the shared secret
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* d. SessionResp1 (DeviceProofM2, dev_rand)
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*
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* Step5. Client (PhoneApp)
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* a. Verify Device
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* Client calculates device proof M2 as M2 = H(A, M, K)
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* verifies this M2 with M2 obtained from device
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*/
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/**
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* @brief Large prime+generator to be used for the algorithm
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*/
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typedef enum {
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/* SRP specific:
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* N = 3072 bit large safe prime,
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* g = generator */
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ESP_NG_3072 = 0,
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} esp_ng_type_t;
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typedef struct esp_srp_handle esp_srp_handle_t;
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/**
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* @brief Initialize srp context for given NG type
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*
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* @param ng NG type given by `esp_ng_type_t`
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* @return esp_srp_handle_t* srp handle
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*
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* @note the handle gets freed with `esp_srp_free`
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*/
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esp_srp_handle_t *esp_srp_init(esp_ng_type_t ng);
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/**
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* @brief free esp_srp_context
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*
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* @param hd handle to be free
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*/
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void esp_srp_free(esp_srp_handle_t *hd);
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/**
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* @brief Returns B (pub key) and salt. [Step2.b]
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*
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* @param hd esp_srp handle
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* @param username Username not expected NULL terminated
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* @param username_len Username length
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* @param pass Password not expected to be NULL terminated
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* @param pass_len Pasword length
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* @param salt_len Salt length
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* @param bytes_B Public Key returned
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* @param len_B Length of the public key
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* @param bytes_salt Salt bytes generated
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* @return esp_err_t ESP_OK on success, appropriate error otherwise
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*
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* @note *bytes_B MUST NOT BE FREED BY THE CALLER
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* @note *bytes_salt MUST NOT BE FREE BY THE CALLER
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*/
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esp_err_t esp_srp_srv_pubkey(esp_srp_handle_t *hd, const char *username, int username_len,
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const char *pass, int pass_len, int salt_len,
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char **bytes_B, int *len_B, char **bytes_salt);
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/**
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* @brief Set the Salt and Verifier pre-generated for a given password.
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*
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* This should be used only if the actual password is not available.
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* The public key can then be generated using esp_srp_srv_pubkey_from_salt_verifier()
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* and not esp_srp_srv_pubkey()
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*
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* @param hd esp_srp_handle
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* @param salt pre-generated salt bytes
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* @param salt_len length of the salt bytes
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* @param verifier pre-generated verifier
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* @param verifier_len length of the verifier bytes
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* @return esp_err_t ESP_OK on success, appropriate error otherwise
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*/
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esp_err_t esp_srp_set_salt_verifier(esp_srp_handle_t *hd, const char *salt, int salt_len,
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const char *verifier, int verifier_len);
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/**
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* @brief Returns B (pub key)[Step2.b] when the salt and verifier are set using esp_srp_set_salt_verifier()
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*
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* @param hd esp_srp handle
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* @param bytes_B Key returned to the called
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* @param len_B Length of the key returned
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* @return esp_err_t ESP_OK on success, appropriate error otherwise
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*
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* @note *bytes_B MUST NOT BE FREED BY THE CALLER
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*/
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esp_err_t esp_srp_srv_pubkey_from_salt_verifier(esp_srp_handle_t *hd, char **bytes_B, int *len_B);
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/**
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* @brief Get session key in `*bytes_key` given by len in `*len_key`. [Step2.c].
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*
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* This calculated session key is used for further communication given the proofs are
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* exchanged/authenticated with `esp_srp_exchange_proofs`
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*
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* @param hd esp_srp handle
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* @param bytes_A Private Key
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* @param len_A Private Key length
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* @param bytes_key Key returned to the caller
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* @param len_key length of the key in *bytes_key
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* @return esp_err_t ESP_OK on success, appropriate error otherwise
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*
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* @note *bytes_key MUST NOT BE FREED BY THE CALLER
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*/
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esp_err_t esp_srp_get_session_key(esp_srp_handle_t *hd, char *bytes_A, int len_A, char **bytes_key, uint16_t *len_key);
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/**
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* @brief Complete the authentication. If this step fails, the session_key exchanged should not be used
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*
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* This is the final authentication step in SRP algorithm [Step4.1, Step4.b, Step4.c]
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*
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* @param hd esp_srp handle
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* @param username Username not expected NULL terminated
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* @param username_len Username length
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* @param bytes_user_proof param in
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* @param bytes_host_proof parameter out (should be SHA512_DIGEST_LENGTH) bytes in size
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* @return esp_err_t ESP_OK if user's proof is ok and subsequently bytes_host_proof is populated with our own proof.
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*/
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esp_err_t esp_srp_exchange_proofs(esp_srp_handle_t *hd, char *username, uint16_t username_len,
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char *bytes_user_proof, char *bytes_host_proof);
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#ifdef __cplusplus
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}
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#endif
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