How can I display/use a control key on iPad Pro?

I want to create a file on Emacs but I got stuck at the final step -saving the file. I know Pressing Ctrl + S will save a file, but the problem is I do not know how to press Ctrl + S on my iPad Pro because it doesn’t show Ctrl key when its keyboard pop up.

soft fork – What is the difference between key aggregation and signature aggregation?

As Pieter Wuille states here key aggregation is completed at address creation time not at signing time or post signing time.

Of course, key aggregation has an impact on the signing algorithm, and that’s probably one of the main reasons why it’s useful to do it before CISA: the work needed to support MuSig signing in wallet will take a while, but it’s pretty similar to CISA signing.

Why is key aggregation better? Because it means the original keys never end up on chain. With signature aggregation you still have on-chain keys, but with 1 signature….Key aggregation means the consensus rules can be completely oblivious of even the concept of aggregation.

Downside: key aggregation cannot be used cross input, as you can’t predict which UTXOs will be spent together.

Meanwhile signature aggregation is completed at signing time or post signing time, not at address creation time. To implement it it would possibly need a specific opcode that observes multiple keys.

Signature aggregation implies a verification algorithm that receives a list of (message,pubkey) pairs and a signature.

You could see key aggregation as a special case of signature aggregation as the aggregated signature is also a valid “single key” signature for the aggregated key. But conceptually there is a huge difference in how they would be implemented.

Why is it important to be careful to use the correct term in its correct setting?

The proposed Taproot soft fork does not enable signature aggregation at all (cross input or otherwise), it facilitates key aggregation schemes e.g. MuSig. As Pieter says the consensus rules of Taproot and Schnorr don’t have any awareness of aggregation. Hence if you say Taproot enables signature aggregation this is incorrect and will confuse. In addition, when moving onto the discussion of what soft fork(s) could potentially follow Taproot, enabling signature aggregation will be a candidate feature that is seriously considered as the block space savings could be immense. Key aggregation allows you to aggregate keys within one input but cross input signature aggregation could potentially allow you to aggregate signatures across inputs. Aggregating signatures not only across inputs but across transactions offers even greater potential block space efficiency savings. At the extreme this could mean only one signature goes onchain for the entire block and all other signatures would not need to be stored or count towards what fills up the block. This would be a massive change though and is unlikely to occur anytime soon.

Keep the foreign key constraint using soft delete

I have a product table and it is foreign key for product ingredients table.

Is there a way to check if it is fk referenced before making isdeleted = true without manually querying for it?

how to keep the foreign key constraint using softdelete

how to keep the foreign key constraint using softdelete? I have a product table and it is foreign key for product ingredients table. Is there a way to check if it is fk referenced before making isdeleted=true without manually query for it

postgresql – Joining two tables partitioned tables having index with the partition key and joining columns does not help much

I have two partitioned tables that have an index created on the joining key and the partition/primary key (because on partitioned tables on Postgres the partition key must belong always to the index). When I run this query:

select
  mol.* 
from merchant_order_lines mol 
where
  mol.fk_x_orders_id = 552369076;

I get the next plan with explain analyze

 Nested Loop  (cost=0.71..3147351.05 rows=419 width=594) (actual time=0.106..727738.027 rows=1 loops=1)


 ->  Index Only Scan using merchant_orders_2017_pkey on merchant_orders_2017 mo  (cost=0.56..8.58 rows=1 width=8) (actual time=0.023..0.026 rows=1 loops=1)
         Index Cond: (sk_id = 552382076)
         Heap Fetches: 1
   ->  Append  (cost=0.14..3147338.27 rows=419 width=594) (actual time=0.079..727737.994 rows=1 loops=1)
         ->  Index Scan using merchant_order_lines_2016_0_sk_id_fk_x_orders_id_idx on merchant_order_lines_2016_0 mol  (cost=0.14..9.28 rows=1 width=514) (actual time=0.031..0.031 r
ows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using merchant_order_lines_2016_1_sk_id_fk_x_orders_id_idx on merchant_order_lines_2016_1 mol_1  (cost=0.14..9.05 rows=1 width=632) (actual time=0.011..0.011
 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using idx_fk_x_orders_id_merchant_order_lines_2017_0 on merchant_order_lines_2017_0 mol_2  (cost=0.56..33.25 rows=84 width=577) (actual time=0.037..0.038 row
s=1 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using merchant_order_lines_2017_1_sk_id_fk_x_orders_id_idx on merchant_order_lines_2017_1 mol_3  (cost=0.56..893039.49 rows=72 width=600) (actual time=198583
.513..198583.513 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using merchant_order_lines_2018_0_sk_id_fk_x_orders_id_idx on merchant_order_lines_2018_0 mol_4  (cost=0.56..1126430.31 rows=130 width=593) (actual time=2836
18.835..283618.835 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using merchant_order_lines_2018_1_sk_id_fk_x_orders_id_idx on merchant_order_lines_2018_1 mol_5  (cost=0.56..1127814.78 rows=131 width=604) (actual time=2455
35.558..245535.558 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
 Planning Time: 14.336 ms
 Execution Time: 727738.113 ms

So the query is using the index (and the ones inherited by the partitions) but I getting and awful time. When I manually create indexes on fk_x_orders_id only per every partition I get the next plan:



 Nested Loop  (cost=0.71..135.21 rows=419 width=594) (actual time=4.232..4.294 rows=1 loops=1)
   ->  Index Only Scan using merchant_orders_2017_pkey on merchant_orders_2017 mo  (cost=0.56..8.58 rows=1 width=8) (actual time=3.431..3.432 rows=1 loops=1)
         Index Cond: (sk_id = 552382076)
         Heap Fetches: 1
   ->  Append  (cost=0.14..122.44 rows=419 width=594) (actual time=0.795..0.855 rows=1 loops=1)
         ->  Index Scan using merchant_order_lines_2016_0_sk_id_fk_x_orders_id_idx on merchant_order_lines_2016_0 mol  (cost=0.14..9.28 rows=1 width=514) (actual
 time=0.010..0.010 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using merchant_order_lines_2016_1_sk_id_fk_x_orders_id_idx on merchant_order_lines_2016_1 mol_1  (cost=0.14..9.05 rows=1 width=632) (actu
al time=0.007..0.007 rows=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using idx_fk_x_orders_id_2017_0 on merchant_order_lines_2017_0 mol_2  (cost=0.56..33.25 rows=84 width=577) (actual time=0.778..0.779 rows
=1 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using idx_fk_x_orders_id_2017_1 on merchant_order_lines_2017_1 mol_3  (cost=0.56..15.51 rows=72 width=600) (actual time=0.017..0.018 rows
=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using idx_fk_x_orders_id_2018_0 on merchant_order_lines_2018_0 mol_4  (cost=0.56..33.38 rows=130 width=593) (actual time=0.020..0.020 row
s=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
         ->  Index Scan using idx_fk_x_orders_id_2018_1 on merchant_order_lines_2018_1 mol_5  (cost=0.56..19.87 rows=131 width=604) (actual time=0.019..0.019 row
s=0 loops=1)
               Index Cond: (fk_x_orders_id = 552382076)
 Planning Time: 0.315 ms
 Execution Time: 4.336 ms

Why does the index that contain the partition/primary key and the column fk_x_orders_id is behaving so badly?

signature – Sign rawtransaction with private key without running a btc node


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encryption – How to get Future Keys (Session Key) from IPEK for decryption data?

I’m new to DUKPT, so I’m not entirely clear about DUKPT and HSM. Right now, I’m trying to decrypt data (PAN number) from terminal.

So far, when I receive KSN and encrypted data, I understand that I need to find encryption key. From my HSM I can get IPEK based on (KSN, BDK). But here is the confusion, based on articles I read, and terminal vendor’s doc, encryption key will be one of the Future Keys.

  1. How would I know which Future Keys terminal uses as encryption key?
  2. How can HSM create Future Keys from IPEK?

Once I get correct Future Keys then I can derive data key variant and do decrypting in my HSM. I’m just stuck with these two questions.

Any explanation would be really helpful.

How can multiple receivers decrypt message with public key

As mentallurg says in his answer, the public key is meant to be public.

I assume the question you mean to ask is “How can someone send a message encrypted to two different recipients, using their public keys?”

The answer is hybrid encryption. The message itself is encrypted with a symmetric key, which I will call the “Data Encryption Key”, or DEK for short. For each recipient, the DEK is then encrypted with the pubic key of the recipient. The public key, used to encrypt the DEK, is sometimes called the “Key Encryption Key”, or KEK for short.

So, for a message sent to two recipients will look like this:

 Key Container 1    Key Container 2    Data Container
┌──────────────────┬──────────────────┬─────────────────────────┐
│ DEK, Encrypted   │ DEK, Encrypted   │ Data, Encrypted with    │
│ w/ public key of │ w/ public key of │ the Data Encryption Key │
│ Recipient #1     │ Recipient #2     │ (DEK)                   │
└──────────────────┴──────────────────┴─────────────────────────┘

The recipient will then see this message, and attempt to decrypt the first key container with every private key they have available. If decryption fails for all of them, they move on to the second container, then the third, and so on, until one of two things happens:

  1. Every key container has been attempted and none could be decrypted.
  2. One container could be decrypted successfully.

In the first case, the decryption fails. In the second case, the DEK will then be used to decrypt the data in question.

Compression algorithm using key value mapping

Compression algorithm using key value mapping – Computer Science Stack Exchange

postgresql – Join two Json arrays to one with key and value

I have two jsonb columns(keys,values).
Eg: keys colum value = ("key1","key2","key3","key4")
values column = ("val1","val2","val3","val4")

I want to write a select query to get the output as below based on the array index.

{"key1":"val1","key2":"val2","key3":"val3","key4":"val4"}

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