Rating:
# Extra careful bank (crypto, 388p)
In the task we get access to a service where we can perform some transactions.
We start with 10$ and we can transfer money to people id 1,2 or 3.
We can do 10 transactions.
We decided to send 1$ 10 times to id 1.
After that we get encrypted listing of all transactions:
```
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
e31da8f33f04cdbf4bfe47bb4854d9761b9e83cfa59aaded8622edf9708db1e350699f75966d4214f5225205504dae0a
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
1b9e83cfa59aaded8622edf9708db1e38bb2ef93e02ef02c91796cc5c4bbaaf0c81f5f0d41e90baa026dd0ced320cabd
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
8bb2ef93e02ef02c91796cc5c4bbaaf0e31da8f33f04cdbf4bfe47bb4854d976376fa414b68f98cee51cda6c80517192
8bb2ef93e02ef02c91796cc5c4bbaaf0e31da8f33f04cdbf4bfe47bb4854d9762cdc7ec92423edf1a807da5f296564ab
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
e31da8f33f04cdbf4bfe47bb4854d9761b9e83cfa59aaded8622edf9708db1e3e41108b58d05256fb242b3d5bc5a095c
1b9e83cfa59aaded8622edf9708db1e3e31da8f33f04cdbf4bfe47bb4854d9765b4737538199cbfbc5b81f2868850830
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
e31da8f33f04cdbf4bfe47bb4854d9761b9e83cfa59aaded8622edf9708db1e3a162ae1d25723cbb5ee1140f5058f246
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
1b9e83cfa59aaded8622edf9708db1e3e31da8f33f04cdbf4bfe47bb4854d976e7c23e7bbb20d587ec9ff0b6b37b0010
1b9e83cfa59aaded8622edf9708db1e38bb2ef93e02ef02c91796cc5c4bbaaf0f5fd11e1b188fa326c39bc7074df95e6
8bb2ef93e02ef02c91796cc5c4bbaaf0e31da8f33f04cdbf4bfe47bb4854d9767306220c74dea23dd6988e22b8a73974
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
```
Notice that we can see 10 times identical string:
```
10c69762f9c25ad18796a8b4ab211ee48bb2ef93e02ef02c91796cc5c4bbaaf07bd8d5142bdc54441fc18622c3c684cb
```
which is probably our ECB-encrypted transaction.
After that we get to see one 500$ transaction:
```
1b9e83cfa59aaded8622edf9708db1e38bb2ef93e02ef02c91796cc5c4bbaaf0e7c1102a0aaff86a691f41f462694eaa
```
Finally we can submit 3 encrypted transactions to get processed, and our goal is to get 1500$.
The system tells us that format of the payload is `sended_id, receiver_id, amount`.
From this we can deduce that:
```
our id -> 10c69762f9c25ad18796a8b4ab211ee4
id1 -> 1b9e83cfa59aaded8622edf9708db1e3
id2 -> 8bb2ef93e02ef02c91796cc5c4bbaaf0
id3 -> e31da8f33f04cdbf4bfe47bb4854d976
500$ -> e7c1102a0aaff86a691f41f462694eaa
```
Therefore we simply forge 3 transactions, to get 500$ from 1,2,3:
```
1b9e83cfa59aaded8622edf9708db1e310c69762f9c25ad18796a8b4ab211ee4e7c1102a0aaff86a691f41f462694eaa
8bb2ef93e02ef02c91796cc5c4bbaaf010c69762f9c25ad18796a8b4ab211ee4e7c1102a0aaff86a691f41f462694eaa
e31da8f33f04cdbf4bfe47bb4854d97610c69762f9c25ad18796a8b4ab211ee4e7c1102a0aaff86a691f41f462694eaa
```
And get the flag: `flag{bank$_sh0uld_n07_us3_ECB}`
