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| 1 | +# Save a Schema and Credential Definition |
| 2 | + |
| 3 | +Indy-SDK Developer Walkthrough #4, Python Edition |
| 4 | + |
| 5 | +[ [Java](../java/README.md) | [.NET](../../not-yet-written.md) | [Node.js](../../not-yet-written.md) | [Objective C](../../not-yet-written.md) ] |
| 6 | + |
| 7 | + |
| 8 | +## Prerequisites |
| 9 | + |
| 10 | +Setup your workstation with an indy development virtual machine (VM). See [prerequisites](../../prerequisites.md). |
| 11 | + |
| 12 | +Ensure you have the 64-bit version of Python 3 installed, as the 32-bit version may have problems loading the Indy .dll files. |
| 13 | + |
| 14 | +## Steps |
| 15 | + |
| 16 | +### Step 1 |
| 17 | + |
| 18 | +In your normal workstation operating system (not the VM), open a Python editor of your |
| 19 | +choice and paste the code from [template.py](template.py) |
| 20 | +into a new doc. We will be modifying this code in later steps. |
| 21 | + |
| 22 | +Save the doc as `save_schema_and_cred_def.py` |
| 23 | + |
| 24 | +This is a very simple app framework into which you'll plug the code you'll be writing. |
| 25 | + |
| 26 | +Install the required python packages by executing: `$ pip install python3-indy asyncio` |
| 27 | + |
| 28 | +### Step 2 |
| 29 | + |
| 30 | +We need to give the SDK some context that it will need |
| 31 | +to deal with an indy ledger. This requires us to point the SDK at some |
| 32 | +*genesis transactions* that tell the SDK how to contact the ledger on |
| 33 | +the network and how to trust that the nodes it contacts possess |
| 34 | +appropriate keys. We also need to create a wallet so the SDK can store |
| 35 | +DIDs and the key material we're going to use. Also, we need |
| 36 | +to create a trust anchor identity that has privileges to create schemas |
| 37 | +and credential definitions. |
| 38 | + |
| 39 | +All of these steps are similar to those in simpler how-tos, such as |
| 40 | +["Write a DID and Query Its Verkey"](../../write-did-and-query-verkey/python/readme.md). |
| 41 | +We'll get this housekeeping out of |
| 42 | +the way in a single step here, rather than dwelling on its details. |
| 43 | + |
| 44 | +Copy the contents of [step2.py](step2.py) into |
| 45 | +`save_schema_and_cred_def.py` on top of the `Step 2 code goes here` placeholder comment. |
| 46 | + |
| 47 | +Save the updated version of `save_schema_and_cred_def.py`. |
| 48 | + |
| 49 | +Study the changes. Scaffolding code like this is likely to appear in anything |
| 50 | +that uses indy. |
| 51 | + |
| 52 | +### Step 3 |
| 53 | + |
| 54 | +Now we need to create and define a schema. Schemas in indy are very simple |
| 55 | +JSON documents that specify their name and version, and that list attributes |
| 56 | +that will appear in a credential. Today, they do not describe data type, |
| 57 | +recurrence rules, nesting, and other elaborate constructs. There is work |
| 58 | +underway to make them fancier; visit |
| 59 | +[#indy-sdk on Rocket.Chat](https://chat.hyperledger.org/channel/indy-sdk) to learn |
| 60 | +more. |
| 61 | + |
| 62 | +A sample schema might look like this: |
| 63 | + |
| 64 | +```json |
| 65 | +{ |
| 66 | + "id": "1", |
| 67 | + "name": "gvt", |
| 68 | + "version": "1.0", |
| 69 | + "ver': "1.0", |
| 70 | + "attrNames": ["age", "sex", "height", "name"] |
| 71 | +} |
| 72 | +``` |
| 73 | + |
| 74 | +Copy the contents of [step3.py](step3.py) into |
| 75 | +`save_schema_and_cred_def.py` on top of the `Step 3 code goes here` placeholder comment. |
| 76 | + |
| 77 | +Save the updated version of `save_schema_and_cred_def.py`. |
| 78 | + |
| 79 | +Notice how this schema is submitted to the ledger by the steward |
| 80 | +identity we created previously. |
| 81 | + |
| 82 | +### Step 4 |
| 83 | + |
| 84 | +Next, we create a *credential definition*. This references the schema |
| 85 | +that we just added, and announces who is going to be issuing credentials |
| 86 | +with that schema (our trust anchor identity, in this case), what type of |
| 87 | +signature method they plan to use ("CL" = "Camenisch Lysyanskya", the |
| 88 | +default method used for zero-knowledge proofs by indy), how they |
| 89 | +plan to handle revocation, and so forth. |
| 90 | + |
| 91 | +Copy the contents of [step4.py](step4.py) into |
| 92 | +`save_schema_and_cred_def.py` on top of the `Step 4 code goes here` placeholder comment. |
| 93 | + |
| 94 | +Save the updated version of `save_schema_and_cred_def.py``. |
| 95 | + |
| 96 | +### Step 5 |
| 97 | + |
| 98 | +Run the [finished code](save_schema_and_cred_def.py) and observe the whole sequence. |
| 99 | + |
| 100 | +## More experiments |
| 101 | + |
| 102 | +You might try the ["Issue a Credential"](../../issue-credential/../not-yet-written.md) |
| 103 | +how-to, which can be done in only one step once you complete this one. |
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