diff --git a/components/wpa_supplicant/esp_supplicant/src/crypto/crypto_mbedtls.c b/components/wpa_supplicant/esp_supplicant/src/crypto/crypto_mbedtls.c index f3f1ba5566..d4c34c8285 100644 --- a/components/wpa_supplicant/esp_supplicant/src/crypto/crypto_mbedtls.c +++ b/components/wpa_supplicant/esp_supplicant/src/crypto/crypto_mbedtls.c @@ -1,5 +1,5 @@ /* - * SPDX-FileCopyrightText: 2020-2023 Espressif Systems (Shanghai) CO LTD + * SPDX-FileCopyrightText: 2020-2025 Espressif Systems (Shanghai) CO LTD * * SPDX-License-Identifier: Apache-2.0 */ @@ -754,7 +754,6 @@ int pbkdf2_sha1(const char *passphrase, const u8 *ssid, size_t ssid_len, int iterations, u8 *buf, size_t buflen) { #ifdef CONFIG_FAST_PBKDF2 - /* For ESP32: Using pbkdf2_hmac_sha1() because esp_fast_psk() utilizes hardware, * but for ESP32, the SHA1 hardware implementation is slower than the software implementation. */ diff --git a/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.c b/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.c index ed92b2c910..2e033f4f7d 100644 --- a/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.c +++ b/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.c @@ -1,5 +1,5 @@ /* - * SPDX-FileCopyrightText: 2015-2024 Espressif Systems (Shanghai) CO LTD + * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD * * SPDX-License-Identifier: Apache-2.0 */ @@ -10,20 +10,61 @@ * Initially authored by Chien Wong(m@xv97.com). */ +/* + * This implementation derives a Pre-Shared Key (PSK) for WPA/WPA2 using a custom PBKDF2-like approach. + * + * PBKDF2 (Password-Based Key Derivation Function 2) is a standard algorithm used to derive cryptographic keys + * from a password and salt. It relies on iteratively applying a pseudorandom function, such as HMAC, to the input. + * The derived key is designed to be computationally expensive to generate, making brute-force attacks more difficult. + * + * In standard PBKDF2, the process is as follows: + * 1. Combine the password and salt (SSID in WPA). + * 2. Compute HMAC for this combination, iteratively applying the previous HMAC output as input for the next iteration. + * 3. XOR all intermediate results to produce the final derived key. + * + * This implementation adapts PBKDF2 for WPA/WPA2 by leveraging the SHA1 hashing algorithm and fixed parameters: + * - The password is up to 63 characters long. + * - The SSID (salt) is up to 32 bytes. + * - The iteration count is fixed at 4096, as required by WPA. + * - The output key length is 32 bytes, suitable for WPA. + * + * Key Differences from Standard PBKDF2: + * - Instead of a general-purpose pseudorandom function, this implementation uses a fixed combination of SHA1 blocks. + * - The logic for handling HMAC is explicitly implemented to optimize for this specific use case. + * - Padding and block alignment are carefully managed to fit within hardware constraints (e.g., the ESP32 SHA1 hardware). + * + * How This Implementation Works: + * 1. The `fast_psk_f` function computes one segment of the derived key. It takes as input: + * - The password. + * - The SSID. + * - A counter value (`count`) that varies for each segment. + * 2. HMAC-SHA1 is implemented explicitly using: + * - An inner padding block (`ipad`) initialized with 0x36 XORed with the password. + * - An outer padding block (`opad`) initialized with 0x5C XORed with the password. + * 3. Intermediate hashes (`U1`, `U2`, ..., `Un`) are computed iteratively. Each `U` value depends on the previous one. + * - `U1` is derived from the password, SSID, and counter. + * - Subsequent `U` values are derived using SHA1 on the previous `U` value. + * 4. All intermediate values are XORed together to produce the final segment of the key. + * 5. The `esp_fast_psk` function combines two invocations of `fast_psk_f` to produce the complete 32-byte key. + * - The first invocation computes the first 16 bytes. + * - The second invocation computes the second 16 bytes. + * + * - The code uses the ESP SHA1 hardware accelerator for faster computation. + */ + #include "fastpsk.h" #include - #include #include #ifndef PUT_UINT32_BE -#define PUT_UINT32_BE(n,b,i) \ +#define PUT_UINT32_BE(n, b, i) \ { \ - (b)[(i) ] = (unsigned char) ( (n) >> 24 ); \ - (b)[(i) + 1] = (unsigned char) ( (n) >> 16 ); \ - (b)[(i) + 2] = (unsigned char) ( (n) >> 8 ); \ - (b)[(i) + 3] = (unsigned char) ( (n) ); \ + (b)[(i)] = (unsigned char)((n) >> 24); \ + (b)[(i) + 1] = (unsigned char)((n) >> 16); \ + (b)[(i) + 2] = (unsigned char)((n) >> 8); \ + (b)[(i) + 3] = (unsigned char)((n)); \ } #endif @@ -35,36 +76,45 @@ #define FAST_PSK_SHA1_BLOCKS_BUF_BYTES (FAST_PSK_SHA1_BLOCKS * SHA1_BLOCK_SZ) #define FAST_PSK_SHA1_BLOCKS_BUF_WORDS (FAST_PSK_SHA1_BLOCKS * SHA1_BLOCK_SZ / 4) +/* Union to represent SHA1 HMAC blocks */ union hmac_block { union { - uint32_t words[SHA1_BLOCK_SZ / 4]; - uint8_t bytes[SHA1_BLOCK_SZ]; + uint32_t words[SHA1_BLOCK_SZ / 4]; /* SHA1 block in words */ + uint8_t bytes[SHA1_BLOCK_SZ]; /* SHA1 block in bytes */ } block[FAST_PSK_SHA1_BLOCKS]; - uint8_t whole_bytes[FAST_PSK_SHA1_BLOCKS_BUF_BYTES]; - uint32_t whole_words[FAST_PSK_SHA1_BLOCKS_BUF_WORDS]; + uint8_t whole_bytes[FAST_PSK_SHA1_BLOCKS_BUF_BYTES]; /* Complete block as bytes */ + uint32_t whole_words[FAST_PSK_SHA1_BLOCKS_BUF_WORDS]; /* Complete block as words */ }; _Static_assert(sizeof(union hmac_block) == 128, "Incorrect layout of hmac_block"); +/* Structure to hold HMAC context */ struct fast_psk_context { - union hmac_block inner, outer; - uint32_t sum[SHA1_OUTPUT_SZ_WORDS]; + union hmac_block inner, outer; /* Inner and outer padding */ + uint32_t sum[SHA1_OUTPUT_SZ_WORDS]; /* Intermediate hash result */ }; +/* Acquire SHA1 hardware for exclusive use */ static inline void sha1_setup(void) { esp_sha_acquire_hardware(); } +/* Release SHA1 hardware */ static inline void sha1_teardown(void) { esp_sha_release_hardware(); } +/* + * Pads the given HMAC block context with the appropriate SHA1 padding. + * Length is the number of bytes of actual data in the block. + */ static void pad_blocks(union hmac_block *ctx, size_t len) { - size_t bits = len << 3; + size_t bits = len << 3; /* Convert length to bits */ uint8_t *bytes = ctx->whole_bytes; - bytes[len] = 0x80; + bytes[len] = 0x80; /* Append 0x80 as per SHA1 padding rules */ + // Set all remaining bytes to 0 memset(&bytes[len + 1], 0, FAST_PSK_SHA1_BLOCKS_BUF_BYTES - (len + 1)); @@ -76,31 +126,53 @@ static void pad_blocks(union hmac_block *ctx, size_t len) PUT_UINT32_BE(bits, bytes, FAST_PSK_SHA1_BLOCKS_BUF_BYTES - 4); } +/* + * Performs SHA1 hash operation on two consecutive blocks. + * Input: blocks array (two blocks of 64 bytes each), output (20-byte digest). + */ void sha1_op(uint32_t blocks[FAST_PSK_SHA1_BLOCKS_BUF_WORDS], uint32_t output[SHA1_OUTPUT_SZ_WORDS]) { + /* First block */ sha_hal_hash_block(SHA1, blocks, SHA1_BLOCK_SZ_WORDS, true); + /* Second block */ sha_hal_hash_block(SHA1, &blocks[SHA1_BLOCK_SZ_WORDS], SHA1_BLOCK_SZ_WORDS, false); + /* Read the final digest */ sha_hal_read_digest(SHA1, output); } +/* + * Implements the PBKDF2-HMAC-SHA1 function for WPA key derivation. + * - password: The passphrase (up to 63 bytes). + * - password_len: Length of the passphrase. + * - ssid: The SSID (up to 32 bytes). + * - ssid_len: Length of the SSID. + * - count: The iteration counter. + * - digest: Output buffer for the resulting digest (20 bytes). + */ void fast_psk_f(const char *password, size_t password_len, const uint8_t *ssid, size_t ssid_len, uint32_t count, uint8_t digest[SHA1_OUTPUT_SZ]) { struct fast_psk_context ctx_, *ctx = &ctx_; size_t i; + /* Clear the context */ memset(ctx, 0, sizeof(*ctx)); + /* Initialize inner and outer padding */ memset(ctx->outer.block[0].bytes, 0x5c, SHA1_BLOCK_SZ); memset(ctx->inner.block[0].bytes, 0x36, SHA1_BLOCK_SZ); + /* XOR the password into the padding */ for (i = 0; i < password_len; ++i) { ctx->outer.block[0].bytes[i] ^= password[i]; ctx->inner.block[0].bytes[i] ^= password[i]; } - // U1 = PRF(P, S || i) + /* Prepare the first input block for HMAC (S || i) */ + /* Copy SSID */ memcpy(ctx->inner.block[1].bytes, ssid, ssid_len); + /* Append the counter */ PUT_UINT32_BE(count, ctx->inner.block[1].bytes, ssid_len); + /* Pad the block */ pad_blocks(&ctx->inner, SHA1_BLOCK_SZ + ssid_len + 4); sha1_setup(); @@ -108,6 +180,7 @@ void fast_psk_f(const char *password, size_t password_len, const uint8_t *ssid, uint32_t *pi, *po; pi = ctx->inner.whole_words; po = ctx->outer.whole_words; + // T1 = SHA1(K ^ ipad, S || i) sha1_op(pi, ctx->outer.block[1].words); @@ -118,16 +191,19 @@ void fast_psk_f(const char *password, size_t password_len, const uint8_t *ssid, uint32_t *sum = ctx->sum; sha1_op(po, inner_blk1); + /* Copy result to the sum */ memcpy(sum, inner_blk1, SHA1_OUTPUT_SZ); pad_blocks(&ctx->inner, SHA1_BLOCK_SZ + SHA1_OUTPUT_SZ); + /* Iterate for remaining 4096 - 1 times */ for (i = 1; i < 4096; ++i) { + /* Compute Tn and Un */ // Tn = SHA1(K ^ ipad, Un-1) sha1_op(pi, outer_blk1); - // Un = SHA1(K ^ opad, Tn) sha1_op(po, inner_blk1); + /* XOR the results to accumulate into F */ // F = U1 ^ U2 ^ ... Un for (size_t j = 0; j < SHA1_OUTPUT_SZ_WORDS; ++j) { sum[j] ^= inner_blk1[j]; @@ -136,19 +212,27 @@ void fast_psk_f(const char *password, size_t password_len, const uint8_t *ssid, sha1_teardown(); + /* Copy the final result to the output digest */ memcpy(digest, sum, SHA1_OUTPUT_SZ); + /* Clear sensitive data */ memset(ctx, 0, sizeof(*ctx)); } int esp_fast_psk(const char *password, size_t password_len, const uint8_t *ssid, size_t ssid_len, size_t iterations, uint8_t *output, size_t output_len) { if (!(ssid_len <= 32 && password_len <= 63 && iterations == 4096 && output_len == 32)) { - return -1; + return -1; /* Invalid input parameters */ } + + /* Compute the first 16 bytes of the PSK */ fast_psk_f(password, password_len, ssid, ssid_len, 2, output); + + /* Replicate the first 16 bytes to form the second half temporarily */ memcpy(output + SHA1_OUTPUT_SZ, output, 32 - SHA1_OUTPUT_SZ); + + /* Compute the second 16 bytes of the PSK */ fast_psk_f(password, password_len, ssid, ssid_len, 1, output); - return 0; + return 0; /* Success */ } diff --git a/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.h b/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.h index 7b0ef58e8c..27de90bd5b 100644 --- a/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.h +++ b/components/wpa_supplicant/esp_supplicant/src/crypto/fastpsk.h @@ -1,5 +1,5 @@ /* - * SPDX-FileCopyrightText: 2015-2024 Espressif Systems (Shanghai) CO LTD + * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD * * SPDX-License-Identifier: Apache-2.0 */