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handle one-octet length headers in public key block reformatting

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This commit is contained in:
Vincent Breitmoser
2017-09-19 15:02:40 +02:00
parent 534f816e35
commit 90b7a0f4f1
2 changed files with 63 additions and 7 deletions
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38
OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpHelper.java
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@@ -44,6 +44,7 @@ public class PgpHelper {
public static final Pattern PGP_PUBLIC_KEY = Pattern.compile(
".*?(-----BEGIN PGP PUBLIC KEY BLOCK-----.*?-----END PGP PUBLIC KEY BLOCK-----).*",
Pattern.DOTALL);
private static final Pattern KEYDATA_START_PATTERN = Pattern.compile("\\s(m[A-Q])");
/**
* Fixing broken PGP MESSAGE Strings coming from GMail/AOSP Mail
@@ -126,17 +127,50 @@ public class PgpHelper {
@Nullable
@CheckResult
@VisibleForTesting
/* Reformats a public key block with messed up whitespace. This will strip headers in the process. */
static String reformatPgpPublicKeyBlock(@NonNull String text) {
StringBuilder reformattedKeyBlocks = new StringBuilder();
/*
This method assumes that the base64 encoded public key data always starts with "m[A-Q]".
This holds based on a few assumptions based on the following observations:
mA encodes 12 bits: 1001 1000 0000
...
mP encodes 12 bits: 1001 1000 1111
mQ encodes 12 bits: 1001 1001 0000
1234 5678
The first bit is a constant 1, the second is 0 for old packet format. Bits 3
through 6 encode the packet tag (constant 6 = b0110). Bits 7 and 8 encode the
length type of the packet, with a value of b00 or b01 referring to a 2- or
3-octet header, respectively. The following four bits are part of the length
header.
Thus we make the following assumptions:
- The packet uses the old packet format. Since the public key packet tag is available in the old format,
there is no reason to use the new one - implementations *could* do that, however.
- The first packet is a public key.
- The length is encoded as one or two bytes.
- If the length is encoded as one byte, the second character may be A through P (four length bits).
- If the length is encoded as two bytes, the second character is Q. This fixes the first four bits of
the length field to zero, limiting the length to 4096.
*/
while (!text.isEmpty()) {
int indexOfBlock = text.indexOf("-----BEGIN PGP PUBLIC KEY BLOCK-----");
int indexOfPubkeyMaterial = text.indexOf("mQ", indexOfBlock);
int indexOfBlockEnd = text.indexOf("-----END PGP PUBLIC KEY BLOCK-----");
if (indexOfBlock < 0 || indexOfPubkeyMaterial < 0 || indexOfBlockEnd < 0) {
if (indexOfBlock < 0 || indexOfBlockEnd < 0) {
break;
}
Matcher matcher = KEYDATA_START_PATTERN.matcher(text);
if (!matcher.find()) {
Log.e(Constants.TAG, "Could not find start of key data!");
break;
}
int indexOfPubkeyMaterial = matcher.start(1);
String keyMaterial = text.substring(indexOfPubkeyMaterial, indexOfBlockEnd);
keyMaterial = keyMaterial.replaceAll("\\s+", "\n");