To address your questions about calculating the checksum in an XFA form:

1. Confirmation of SHA-1 Algorithm

Yes, the checksum attribute in Adobe's XFA forms is generated using the SHA-1 hashing algorithm. This value is a hexadecimal representation of the SHA-1 digest computed over specific XFA data.

2. Data Used to Generate the Checksum

The checksum is derived from hashing the **seri...

Short answer

• Yes. It’s a SHA‑1 digest (20 bytes), written as a 40‑character lowercase hex string.
• It is not computed over the data you export. It is computed over the form design (the XFA template packet).

What to hash exactly Adobe computes the checksum over the XFA template (the packet named template in the XFA/XDP, i.e., the form design), not over the datasets/data you are saving. The purp...

Short answer

1. Yes – the value that Adobe puts into the checksum attribute is a standard 160-bit SHA-1 message digest.
2. What is hashed is the canonical byte sequence of the packet (template, form, datasets, config, …) that owns the attribute, not the whole PDF file and not the XFA container as a whole.
   Before the digest is written the 20 raw digest bytes are Base-64 encoded, whic...

How to Calculate the Checksum in an XFA Form

The checksum attribute in XFA forms is indeed a point of confusion since it's not documented in the official XFA specification. Based on my understanding of Adobe's implementation:

Is it a SHA-1 hash?

Yes, the checksum is typically a SHA-1 hash value, which is why you're seeing what appears to be a 40-character hexadecimal string.

What data ...

Here’s what you need to know:

1. Yes – that 40-character checksum is nothing more exotic than a SHA-1 digest (20 bytes, hex-encoded).

2. What you hash is the raw XML of the XFA “datasets” packet exactly as Acrobat wrote it, but with the checksum attribute itself removed (or blanked). In practice that means:

   a. Extract the XDP (or the XFA stream) from the PDF and find the `<xfa:datasets ...

<think> We are given a question about calculating the checksum in an XFA form. The user has observed that when saving an XFA form with Adobe software, a checksum attribute is added to the form element. They suspect it is a SHA-1 digest but are unsure of the exact data that is hashed. The goal is to:

1. Confirm whether the checksum is indeed a SHA-1 hash.
2. Explain what data should be used to cre...

Here is a detailed, well-structured answer in the style of Stack Overflow, addressing the user's question.

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Title: How to calculate the checksum in an XFA form

You've run into a classic problem when programmatically generating XFA forms. That checksum attribute is an undocumented, proprietary feature used by Adobe software to verify the integrity of the form's template and data.

Here ...

The checksum attribute in XFA forms is indeed a SHA-1 hash, but determining exactly what data is hashed can be tricky since, as you noted, it's not documented in the official XFA specification.

1. Confirmation of SHA-1 Algorithm

Yes, the checksum is typically a SHA-1 hash. This can be confirmed by:

• The length of the checksum (40 hexadecimal characters = 160 bits = SHA-1 output)
• Reverse en...

Adobe adds the checksum merely to be able to find out later whether a particular XFA packet has been changed.
It is not a security feature – it is only a “did-anything-inside-this-packet change?” flag – and therefore it is not described in the public XFA specification.

1. Which algorithm is used?
   • It is SHA-1.
   The 20-byte digest is written as 40 lower-case hexadecimal digi...