diff options
Diffstat (limited to 'aes_keywrap.c')
| -rw-r--r-- | aes_keywrap.c | 300 |
1 files changed, 300 insertions, 0 deletions
diff --git a/aes_keywrap.c b/aes_keywrap.c new file mode 100644 index 0000000..fc1c1bd --- /dev/null +++ b/aes_keywrap.c @@ -0,0 +1,300 @@ +/* + * Implementation of RFC 5649 variant of AES Key Wrap, using Cryptlib + * to supply the AES ECB encryption and decryption functions. + * + * Note that there are two different block sizes involved here: the + * key wrap algorithm deals entirely with 64-bit blocks, while AES + * itself deals with 128-bit blocks. In practice, this is not as + * confusing as it sounds, because we combine two 64-bit blocks to + * create one 128-bit block just prior to performing an AES operation, + * then split the result back to 64-bit blocks immediately afterwards. + */ + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <assert.h> + +#include <cryptlib.h> + +#include "aes_keywrap.h" + +aes_key_wrap_status_t aes_key_wrap(const CRYPT_CONTEXT K, + const unsigned char * const Q, + const size_t m, + unsigned char *C, + size_t *C_len) +{ + unsigned char aes_block[16]; + unsigned long n; + long i, j; + + assert(AES_KEY_WRAP_CIPHERTEXT_SIZE(m) % 8 == 0); + + if (Q == NULL || C == NULL || C_len == NULL || *C_len < AES_KEY_WRAP_CIPHERTEXT_SIZE(m)) + return AES_KEY_WRAP_BAD_ARGUMENTS; + + *C_len = AES_KEY_WRAP_CIPHERTEXT_SIZE(m); + + memmove(C + 8, Q, m); + if (m % 8 != 0) + memset(C + 8 + m, 0, 8 - (m % 8)); + C[0] = 0xA6; + C[1] = 0x59; + C[2] = 0x59; + C[3] = 0xA6; + C[4] = (m >> 24) & 0xFF; + C[5] = (m >> 16) & 0xFF; + C[6] = (m >> 8) & 0xFF; + C[7] = (m >> 0) & 0xFF; + + n = (AES_KEY_WRAP_CIPHERTEXT_SIZE(m) / 8) - 1; + + if (n == 1) { + if (cryptEncrypt(K, C, 16) != CRYPT_OK) + return AES_KEY_WRAP_ENCRYPTION_FAILED; + } + + else { + for (j = 0; j <= 5; j++) { + for (i = 1; i <= n; i++) { + unsigned long t = n * j + i; + memcpy(aes_block + 0, C, 8); + memcpy(aes_block + 8, C + i * 8, 8); + if (cryptEncrypt(K, aes_block, sizeof(aes_block)) != CRYPT_OK) + return AES_KEY_WRAP_ENCRYPTION_FAILED; + memcpy(C, aes_block + 0, 8); + memcpy(C + i * 8, aes_block + 8, 8); + C[7] ^= t & 0xFF; t >>= 8; + C[6] ^= t & 0xFF; t >>= 8; + C[5] ^= t & 0xFF; t >>= 8; + C[4] ^= t & 0xFF; + } + } + } + + return AES_KEY_WRAP_OK; +} + +aes_key_wrap_status_t aes_key_unwrap(const CRYPT_CONTEXT K, + const unsigned char * const C, + const size_t C_len, + unsigned char *Q, + size_t *Q_len) +{ + unsigned char aes_block[16]; + unsigned long n; + long i, j; + size_t m; + + if (C == NULL || Q == NULL || C_len % 8 != 0 || C_len < 16 || Q_len == NULL || *Q_len < C_len) + return AES_KEY_WRAP_BAD_ARGUMENTS; + + n = (C_len / 8) - 1; + + if (Q != C) + memmove(Q, C, C_len); + + if (n == 1) { + if (cryptDecrypt(K, Q, 16) != CRYPT_OK) + return AES_KEY_WRAP_DECRYPTION_FAILED; + } + + else { + for (j = 5; j >= 0; j--) { + for (i = n; i >= 1; i--) { + unsigned long t = n * j + i; + Q[7] ^= t & 0xFF; t >>= 8; + Q[6] ^= t & 0xFF; t >>= 8; + Q[5] ^= t & 0xFF; t >>= 8; + Q[4] ^= t & 0xFF; + memcpy(aes_block + 0, Q, 8); + memcpy(aes_block + 8, Q + i * 8, 8); + if (cryptDecrypt(K, aes_block, sizeof(aes_block)) != CRYPT_OK) + return AES_KEY_WRAP_DECRYPTION_FAILED; + memcpy(Q, aes_block + 0, 8); + memcpy(Q + i * 8, aes_block + 8, 8); + } + } + } + + if (Q[0] != 0xA6 || Q[1] != 0x59 || Q[2] != 0x59 || Q[3] != 0xA6) + return AES_KEY_WRAP_BAD_MAGIC; + + m = (((((Q[4] << 8) + Q[5]) << 8) + Q[6]) << 8) + Q[7]; + + if (m <= 8 * (n - 1) || m > 8 * n) + return AES_KEY_WRAP_BAD_LENGTH; + + if (m % 8 != 0) + for (i = m + 8; i < 8 * (n + 1); i++) + if (Q[i] != 0x00) + return AES_KEY_WRAP_BAD_PADDING; + + *Q_len = m; + + memmove(Q, Q + 8, m); + + return AES_KEY_WRAP_OK; +} + +const char *aes_key_wrap_error_string(const aes_key_wrap_status_t code) +{ + switch (code) { + case AES_KEY_WRAP_OK: return "OK"; + case AES_KEY_WRAP_BAD_ARGUMENTS: return "Bad argument"; + case AES_KEY_WRAP_ENCRYPTION_FAILED: return "Encryption failed"; + case AES_KEY_WRAP_DECRYPTION_FAILED: return "Decryption failed"; + case AES_KEY_WRAP_BAD_MAGIC: return "Bad AIV magic number"; + case AES_KEY_WRAP_BAD_LENGTH: return "Encoded length out of range"; + case AES_KEY_WRAP_BAD_PADDING: return "Nonzero padding detected"; + default: return NULL; + } +} + + +#ifdef AES_KEY_WRAP_SELF_TEST + +/* + * Test cases from RFC 5649. + */ + +typedef struct { + const char *K; /* Key-encryption-key */ + const char *Q; /* Plaintext */ + const char *C; /* Ciphertext */ +} test_case_t; + +static const test_case_t test_case[] = { + + { "5840df6e29b02af1 ab493b705bf16ea1 ae8338f4dcc176a8", /* K */ + "c37b7e6492584340 bed1220780894115 5068f738", /* Q */ + "138bdeaa9b8fa7fc 61f97742e72248ee 5ae6ae5360d1ae6a 5f54f373fa543b6a"}, /* C */ + + { "5840df6e29b02af1 ab493b705bf16ea1 ae8338f4dcc176a8", /* K */ + "466f7250617369", /* Q */ + "afbeb0f07dfbf541 9200f2ccb50bb24f" } /* C */ + +}; + +static int parse_hex(const char *hex, unsigned char *bin, size_t *len, const size_t max) +{ + static const char whitespace[] = " \t\r\n"; + size_t i; + + assert(hex != NULL && bin != NULL && len != NULL); + + hex += strspn(hex, whitespace); + + for (i = 0; *hex != '\0' && i < max; i++, hex += 2 + strspn(hex + 2, whitespace)) + if (sscanf(hex, "%2hhx", &bin[i]) != 1) + return 0; + + *len = i; + + return *hex == '\0'; +} + +static const char *format_hex(const unsigned char *bin, const size_t len, char *hex, const size_t max) +{ + size_t i; + + assert(bin != NULL && hex != NULL && len * 3 < max); + + if (len == 0) + return ""; + + for (i = 0; i < len; i++) + sprintf(hex + 3 * i, "%02x:", bin[i]); + + hex[len * 3 - 1] = '\0'; + return hex; +} + +#ifndef TC_BUFSIZE +#define TC_BUFSIZE 4096 +#endif + +static int run_test(const test_case_t * const tc) +{ + unsigned char K[TC_BUFSIZE], Q[TC_BUFSIZE], C[TC_BUFSIZE], q[TC_BUFSIZE], c[TC_BUFSIZE]; + size_t K_len, Q_len, C_len, q_len = sizeof(q), c_len = sizeof(c); + char h1[TC_BUFSIZE * 3], h2[TC_BUFSIZE * 3]; + aes_key_wrap_status_t ret; + CRYPT_CONTEXT ctx; + int ok = 1; + + assert(tc != NULL); + + if (!parse_hex(tc->K, K, &K_len, sizeof(K))) + return printf("couldn't parse KEK %s\n", tc->K), 0; + + if (!parse_hex(tc->Q, Q, &Q_len, sizeof(Q))) + return printf("couldn't parse plaintext %s\n", tc->Q), 0; + + if (!parse_hex(tc->C, C, &C_len, sizeof(C))) + return printf("couldn't parse ciphertext %s\n", tc->C), 0; + + if (cryptCreateContext(&ctx, CRYPT_UNUSED, CRYPT_ALGO_AES) != CRYPT_OK) + return printf("couldn't create context\n"), 0; + + if (cryptSetAttribute(ctx, CRYPT_CTXINFO_MODE, CRYPT_MODE_ECB) != CRYPT_OK || + cryptSetAttributeString(ctx, CRYPT_CTXINFO_KEY, K, K_len) != CRYPT_OK) + ok = printf("couldn't initialize KEK\n"), 0; + + if (ok) { + + if ((ret = aes_key_wrap(ctx, Q, Q_len, c, &c_len)) != AES_KEY_WRAP_OK) + ok = printf("couldn't wrap %s: %s\n", tc->Q, aes_key_wrap_error_string(ret)), 0; + + if ((ret = aes_key_unwrap(ctx, C, C_len, q, &q_len)) != AES_KEY_WRAP_OK) + ok = printf("couldn't unwrap %s: %s\n", tc->C, aes_key_wrap_error_string(ret)), 0; + + if (C_len != c_len || memcmp(C, c, C_len) != 0) + ok = printf("ciphertext mismatch:\n Want: %s\n Got: %s\n", + format_hex(C, C_len, h1, sizeof(h1)), + format_hex(c, c_len, h2, sizeof(h2))), 0; + + if (Q_len != q_len || memcmp(Q, q, Q_len) != 0) + ok = printf("plaintext mismatch:\n Want: %s\n Got: %s\n", + format_hex(Q, Q_len, h1, sizeof(h1)), + format_hex(q, q_len, h2, sizeof(h2))), 0; + + } + + cryptDestroyContext(ctx); + return ok; +} + +int main (int argc, char *argv[]) +{ + int i; + + if (cryptInit() != CRYPT_OK) + return printf("Couldn't initialize Cryptlib\n"), 1; + + for (i = 0; i < sizeof(test_case)/sizeof(*test_case); i++) { + printf("Running test case #%d...", i); + if (run_test(&test_case[i])) + printf("OK\n"); + } + + if (cryptEnd() != CRYPT_OK) + return printf("Cryptlib unhappy on shutdown\n"), 1; + + return 0; +} + +#endif + +/* + * "Any programmer who fails to comply with the standard naming, formatting, + * or commenting conventions should be shot. If it so happens that it is + * inconvenient to shoot him, then he is to be politely requested to recode + * his program in adherence to the above standard." + * -- Michael Spier, Digital Equipment Corporation + * + * Local variables: + * indent-tabs-mode: nil + * End: + */ |