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Replace manual concatenation with actual ASN.1 encoder #78

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merged 3 commits into from
Mar 10, 2024
Merged

Replace manual concatenation with actual ASN.1 encoder #78

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744998e
Add reference for OID source
Firehed Mar 10, 2024
3ad7a89
Add lib
Firehed Mar 10, 2024
49006e6
Replace cryptic manual encoding with an actual tool
Firehed Mar 10, 2024
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3 changes: 2 additions & 1 deletion composer.json
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,8 @@
"ext-gmp": "*",
"ext-hash": "*",
"ext-openssl": "*",
"firehed/cbor": "^0.1.0"
"firehed/cbor": "^0.1.0",
"sop/asn1": "^4.1"
},
"require-dev": {
"maglnet/composer-require-checker": "^4.1",
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2 changes: 2 additions & 0 deletions src/COSE/Curve.php
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Expand Up @@ -36,6 +36,8 @@ enum Curve: int

case ED448 = 7; // OKP

// RFC 5480
// §2.1.1.1 OIDs for named curves
public function getOid(): string
{
return match ($this) {
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30 changes: 15 additions & 15 deletions src/PublicKey/EllipticCurve.php
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Expand Up @@ -9,6 +9,7 @@
use Firehed\WebAuthn\COSE;
use Firehed\WebAuthn\COSEKey;
use Firehed\WebAuthn\Errors\VerificationError;
use Sop\ASN1\Type as ASN;
use UnexpectedValueException;

use function gmp_pow;
Expand All @@ -31,6 +32,8 @@
*/
class EllipticCurve implements PublicKeyInterface
{
private const OID = '1.2.840.10045.2.1';

// CBOR decoding: RFC 9053 §7.1.1
private const INDEX_CURVE = -1; // ECC, OKP
private const INDEX_X_COORDINATE = -2; // ECC, OKP
Expand Down Expand Up @@ -121,22 +124,19 @@ public function getPemFormatted(): string
if ($this->curve !== COSE\Curve::P256) {
throw new DomainException('Only P256 curves can be PEM-formatted so far');
}
// Described in RFC 5480
// §2.1.1.1
// Just use an OID calculator to figure out *that* encoding
$der = hex2bin(
'3059' // SEQUENCE, length 89
. '3013' // SEQUENCE, length 19
. '0607' // OID, length 7
. '2a8648ce3d0201' // 1.2.840.10045.2.1 = EC Public Key
. '0608' // OID, length 8
. '2a8648ce3d030107' // 1.2.840.10045.3.1.7 = P-256 Curve
. '0342' // BIT STRING, length 66
. '00' // prepend with NUL
. '04' // uncompressed format

$asn = new ASN\Constructed\Sequence(
new ASN\Constructed\Sequence(
new ASN\Primitive\ObjectIdentifier(self::OID),
new ASN\Primitive\ObjectIdentifier($this->curve->getOid()),
),
new ASN\Primitive\BitString(
"\x04" // Uncompressed
. $this->x->unwrap()
. $this->y->unwrap(),
),
);
$der .= $this->x->unwrap();
$der .= $this->y->unwrap();
$der = $asn->toDER();

$pem = "-----BEGIN PUBLIC KEY-----\n";
$pem .= chunk_split(base64_encode($der), 64, "\n");
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