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Fix TPM2_ASN_TrimZeros skipping bytes #644

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Merged
dgarske merged 1 commit into from
Oct 21, 2026
Merged

Fix TPM2_ASN_TrimZeros skipping bytes #644

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3 changes: 1 addition & 2 deletions src/tpm2_asn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -34,10 +34,9 @@ byte* TPM2_ASN_TrimZeros(byte* in, word32* len)
word32 idx = 0;
while (idx+1 < *len && in[idx] == 0 && (in[idx+1] & 0x80) == 0) {
idx++;
in++;
}
*len -= idx;
return in;
return in + idx;
}

int TPM2_ASN_GetLength_ex(const uint8_t* input, word32* inOutIdx, int* len,
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31 changes: 31 additions & 0 deletions tests/unit_tests.c
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Expand Up @@ -8840,6 +8840,36 @@ static void test_TPM2_ASN_RsaUnpadPkcsv15(void)
#endif
}

static void test_TPM2_ASN_TrimZeros(void)
{
#if !defined(WOLFTPM2_NO_WRAPPER) && !defined(WOLFTPM2_NO_ASN)
/* ECDSA S from a failed CI run: only the first zero may go */
byte s[] = { 0x00, 0x71, 0x00, 0x4F, 0x95 };
byte hi[] = { 0x00, 0x80, 0x01 };
byte two[] = { 0x00, 0x00, 0x05 };
byte* p;
word32 len;

len = (word32)sizeof(s);
p = TPM2_ASN_TrimZeros(s, &len);
AssertIntEQ(len, 4);
AssertTrue(p == &s[1]);

/* A zero before a high bit byte is kept */
len = (word32)sizeof(hi);
p = TPM2_ASN_TrimZeros(hi, &len);
AssertIntEQ(len, 3);
AssertTrue(p == &hi[0]);

len = (word32)sizeof(two);
p = TPM2_ASN_TrimZeros(two, &len);
AssertIntEQ(len, 1);
AssertTrue(p == &two[2]);

printf("Test TPM Wrapper: %-40s Passed\n", "ASN TrimZeros:");
#endif
}

#if !defined(WOLFTPM2_NO_WRAPPER) && !defined(WOLFTPM2_NO_ASN)
#include <examples/endorsement/trusted_certs_der.h>
#endif
Expand Down Expand Up @@ -11371,6 +11401,7 @@ int unit_tests(int argc, char *argv[])
test_wolfTPM2_CryptoDevCb_MlDsaKeyId();
test_TPM2_ASN_DecodeX509Cert_Errors();
test_TPM2_ASN_RsaUnpadPkcsv15();
test_TPM2_ASN_TrimZeros();
test_TPM2_ASN_DecodeX509Cert_Valid();
test_TPM2_ASN_DecodeTag_Errors();
#if !defined(WOLFTPM2_NO_WOLFCRYPT) && defined(WOLFTPM2_PEM_DECODE) && \
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