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fix: RSA from JWK sometimes returns empty Instance #628

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fix: RSA from JWK sometimes returns empty Instance #628

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fix: RSA from JWK sometimes returns empty Instance
NReib Mar 27, 2026
50a3ef0
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NReib Mar 27, 2026
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8 changes: 8 additions & 0 deletions src/JWK.php
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,14 @@ private static function createPemFromModulusAndExponent(
): string {
$mod = JWT::urlsafeB64Decode($n);
$exp = JWT::urlsafeB64Decode($e);
// Correct encoding for ASN1, as ints are represented as unsigned in jwk
// but signed in ASN1. Prepending null byte makes it unsigned.
if (\strlen($mod) > 0 && \ord($mod[0]) >= 128) {
$mod = \chr(0) . $mod;
}
if (\strlen($exp) > 0 && \ord($exp[0]) >= 128) {
$exp = \chr(0) . $exp;
}

$modulus = \pack('Ca*a*', 2, self::encodeLength(\strlen($mod)), $mod);
$publicExponent = \pack('Ca*a*', 2, self::encodeLength(\strlen($exp)), $exp);
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