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[release/9.0-staging] [Android] Normalize RSA no-padding output to modulus size to fix VerifyHash #118926

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[release/9.0-staging] [Android] Normalize RSA no-padding output to modulus size to fix VerifyHash #118926

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11 changes: 9 additions & 2 deletions src/native/libs/System.Security.Cryptography.Native.Android/pal_rsa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -327,14 +327,21 @@ PALEXPORT int32_t AndroidCryptoNative_RsaVerificationPrimitive(int32_t flen, uin
}

jsize decryptedBytesLen = (*env)->GetArrayLength(env, decryptedBytes);
(*env)->GetByteArrayRegion(env, decryptedBytes, 0, decryptedBytesLen, (jbyte*) to);
abort_unless(decryptedBytesLen <= flen, "Decrypted bytes length %d exceeds expected length %d", decryptedBytesLen, flen);

// In some versions of the Android crypto libraries, the leading 0x00 bytes are missing.
// Left-pad with 0x00 so EM is always k bytes (k = modulus), as expected by .NET.
int32_t leading_zero_padding_length = flen - decryptedBytesLen;
memset(to, 0x00, (size_t)leading_zero_padding_length);

(*env)->GetByteArrayRegion(env, decryptedBytes, 0, decryptedBytesLen, (jbyte*)to + leading_zero_padding_length);

(*env)->DeleteLocalRef(env, cipher);
(*env)->DeleteLocalRef(env, fromBytes);
(*env)->DeleteLocalRef(env, decryptedBytes);
(*env)->DeleteLocalRef(env, algName);

return (int32_t)decryptedBytesLen;
return (int32_t)decryptedBytesLen + leading_zero_padding_length;
}

PALEXPORT int32_t AndroidCryptoNative_RsaGenerateKeyEx(RSA* rsa, int32_t bits)
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