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Posted to dev@pdfbox.apache.org by "Štěpán Schejbal (JIRA)" <ji...@apache.org> on 2014/06/16 18:00:02 UTC
[jira] [Updated] (PDFBOX-2082) signing corrupts PDF when signature
exactly fits allocated space
[ https://issues.apache.org/jira/browse/PDFBOX-2082?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Štěpán Schejbal updated PDFBOX-2082:
------------------------------------
Affects Version/s: 2.0.0
1.8.5
> signing corrupts PDF when signature exactly fits allocated space
> ----------------------------------------------------------------
>
> Key: PDFBOX-2082
> URL: https://issues.apache.org/jira/browse/PDFBOX-2082
> Project: PDFBox
> Issue Type: Bug
> Components: Writing
> Affects Versions: 1.8.5, 1.8.6, 2.0.0
> Reporter: Štěpán Schejbal
> Priority: Critical
> Labels: patch
>
> The current check does not take "<>" into account, so if you are (un)lucky, the signature overwrites ">" and corrupts the PDF.
> Fix for 1.8:
> {code}
> diff --git a/pdfbox/src/main/java/org/apache/pdfbox/pdfwriter/COSWriter.java b/pdfbox/src/main/java/org/apache/pdfbox/pdfwriter/COSWriter.java
> index 3165589..80fbad2 100644
> --- a/pdfbox/src/main/java/org/apache/pdfbox/pdfwriter/COSWriter.java
> +++ b/pdfbox/src/main/java/org/apache/pdfbox/pdfwriter/COSWriter.java
> @@ -778,13 +778,15 @@ public class COSWriter implements ICOSVisitor, Closeable
>
> SignatureInterface signatureInterface = doc.getSignatureInterface();
> byte[] sign = signatureInterface.sign(new ByteArrayInputStream(pdfContent));
> + // this assumes that the dummy signature has been writen as "<0000...>"
> String signature = new COSString(sign).getHexString();
> - int leftSignaturerange = signaturePosition[1]-signaturePosition[0]-signature.length();
> - if(leftSignaturerange<0)
> + int startPos = signaturePosition[0] + 1; // move past "<"
> + int endPos = signaturePosition[1] - 1; // move in front of ">"
> + if (startPos + signature.length() > endPos)
> {
> throw new IOException("Can't write signature, not enough space");
> }
> - getStandardOutput().setPos(signaturePosition[0]+1);
> + getStandardOutput().setPos(startPos);
> getStandardOutput().write(signature.getBytes());
> }
> }
> {code}
> Another thing is that pdfbox now allocates (2 * preferedSize + 2) for a signature. It quite confused me to see 16k+4 bytes allocated when I called setPreferedSignatureSize(4k) - it should have allocated 8k (each signature byte takes 2 bytes in the pdf).
> Fix for 1.8:
> {code}
> diff --git a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
> index 358364a..23dd3ab 100644
> --- a/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
> +++ b/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/PDDocument.java
> @@ -309,7 +309,7 @@ public class PDDocument implements Pageable, Closeable
> int preferedSignatureSize = options.getPreferedSignatureSize();
> if (preferedSignatureSize > 0)
> {
> - sigObject.setContents(new byte[preferedSignatureSize * 2 + 2]);
> + sigObject.setContents(new byte[preferedSignatureSize]);
> }
> else
> {
> {code}
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