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Update NanoTDF spec to handle ECSDA signature with different r and s value sizes #17

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Update NanoTDF spec to handle ECSDA signature with different r and s value sizes #17

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606 changes: 605 additions & 1 deletion diagrams/nanotdf.svg
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35 changes: 25 additions & 10 deletions schema/nanotdf/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -278,7 +278,7 @@ private key and the resulting signature. The structure of this section:
| Section | Minimum Length (B) | Maximum Length (B) |
|---------------|---------------------|---------------------|
| Public Key | 33 | 67 |
| Signature | 64 | 132 |
| Signature | 66 | 134 |

##### 3.3.3.1 Public Key

Expand All @@ -287,7 +287,7 @@ the message.

##### 3.3.3.2 Signature

This section contains the encoded `r` and `s` values of the ECDSA signature.
This section contains the size of `r` and `s` and encoded `r` and `s` values of the ECDSA signature.
They are encoded as described in [Section 5.2].

### 3.4 nanotdf Types
Expand Down Expand Up @@ -483,18 +483,33 @@ the X9.62 ECC Public Key Compressed Encoding format.

[Section 5.2]: #52-ecdsa-signature-encoding

ECDSA signatures are big endian encodings of the `r` and `s` values of an ECDSA
signature. The length of `r` and `s` values is determined by the ECC Mode used
for the signature. The encoding for the signature is the big endian encodings of
R and S concatenated to each other. For example, `r = 1` and `s = 2` for an
The structure of this section is as follows:

| Section | Minimum Length (B) | Maximum Length (B) |
|------------------------|--------------------|---------------------|
| Size of 'r' value | 1 | 1 |
| ECDSA 'r' value | 33 | 67 |
| Size of 's' value | 1 | 1 |
| ECDSA 's' value | 33 | 67 |


ECDSA signature 'r' and 's' values are big endian encoding.
The length of `r` and `s` values is determined by the ECC Mode used for the signature.

NOTE: 'r' and 's' value need not be of same length for example for curve secp256k1,
the size of 'r' value can be 31 bytes and 's' value can be of 32 bytes. In this
case the 'r' value is padded with '0x0'

For example, `r = 1` and `s = 2` for an
ECDSA signature of a secp256k1 key would be (line breaks and spaces are added
for easier visualization):

```
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02
01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 02
```

## 6. Examples
Expand Down