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fix: also compress key on iOS when fallback secure environment is used #18

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merged 1 commit into from
Nov 22, 2024
Merged

fix: also compress key on iOS when fallback secure environment is used #18

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34 changes: 21 additions & 13 deletions src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,34 +12,42 @@ export async function generateKeypair(id: string, biometricsBacked = true): Prom

export async function getPublicBytesForKeyId(keyId: string): Promise<Uint8Array> {
const publicBytes = await getSecureEnvironment().getPublicBytesForKeyId(keyId)
let uncompressedKey = publicBytes
let key = publicBytes

if (Platform.OS === 'android' && publicBytes.length > 65) {
if (key.length > 65) {
// Try to parse it from the ASN.1 SPKI format
const spki = AsnParser.parse(publicBytes, SubjectPublicKeyInfo)
uncompressedKey = new Uint8Array(spki.subjectPublicKey)
key = new Uint8Array(spki.subjectPublicKey)
}

if (Platform.OS === 'android') {
if (uncompressedKey.length !== 65 || uncompressedKey[0] !== 0x04) {
throw new Error('Invalid uncompressed key format')
}
if (key.length === 65 && key[0] !== 0x04) {
throw new Error('Invalid uncompressed key prefix')
}

if (key.length === 65) {
// Extract the X and Y coordinates
const x = uncompressedKey.slice(1, 33) // bytes 1 to 32 (X coordinate)
const y = uncompressedKey.slice(33, 65) // bytes 33 to 64 (Y coordinate)

const x = key.slice(1, 33) // bytes 1 to 32 (X coordinate)
const y = key.slice(33, 65) // bytes 33 to 64 (Y coordinate)
// Determine the parity of the Y coordinate
const prefix = y[y.length - 1] % 2 === 0 ? 0x02 : 0x03

// Return the compressed key (prefix + X coordinate)
const compressedKey = new Uint8Array(33)
compressedKey[0] = prefix
compressedKey.set(x, 1)
return compressedKey
key = compressedKey
}

if (key.length === 33 && key[0] !== 0x03 && key[0] !== 0x02) {
throw new Error('Invalid compressed key prefix')
}

if (key.length !== 33) {
throw new Error(
`After attempting key compression, the key has an invalid length. Expected: '33', Received: '${key.length}'`
)
}

return publicBytes
return key
}

export async function sign(keyId: string, message: Uint8Array, biometricsBacked = true): Promise<Uint8Array> {
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