Boxcryptor is using AES and RSA to encrypt files. Thats safe.
But how they implemented the algorithm and whether they made any mistakes (or backdoor) in the implementation can't be told for sure without inspecting the source code.
I would rather switch to a tool which has its source code published and read dozens of time. Veracrypt[1] (the successor of truecrypt) would be a trustworthy open-source alternative.
[1] Veracrypt: https://veracrypt.codeplex.com/; Source: https://veracrypt.codeplex.com/SourceControl/latest#README.md

To get the real maximum amount of transactions being possibly in one block:
Consider a block filled with the smallest possible (segwit-)transactions (1 input / 1 output)
The real crucial point is the sum of the non-witness part.
With 82 byte (non-witness part) transactions and a non-witness blocksize of 1MB we get a maximum of 12.195 transactions / block.
Compared to the corresponding non-segwit transactions (with size of 192 byte) this would be a maximum of 5.208 transaction / block.
Please note: This is an extreme example, since TX's mostly aren't only made of 1 input / 1 output. But it shows the limit of transactions (currently) possible.

Of course. There is no reason why this shouldn't be doable in C. I guess you are planning to use libaries instead of doing this from scratch.
You can use LIBBTC (https://github.com/libbtc/libbtc). But make sure how generation is exactly handled and how entropy is gathered.
And if you want to store larger amounts on your selfwritten wallet, make sure to catch any exceptions and create a testing environment to make sure it works properly in every case.

If your balance is still right (dont forget the transaction fee), then your coins got send to a change address.
You can click the link posted above to read more about how the change works in BTC.

But if your balance is wrong and 0.002 btc are missing:

Did you create a wallet with 2-factor-authentication?



In this case TrustedCoin charges a fee of 0.0001 btc (being prepayed for 20 tx's => 0.002 btc) for co-signing your transaction.
Did you click through without reading?



You can read more about it here: https://api.trustedcoin.com/#/electrum-help

First of all, there is no 'legacy blockchain' and no 'segwit blockchain'. It is bitcoin, it is one blockchain.
You can 'store your coins' in either 1) a legacy address or 2) an address in segwit format.
The fees of BTC are going higher if more people want to send coins around and are ready to pay more for that.
And if people decide to not send too much across the BTC network (and are not ready to pay 30$ for a TX), the median price of a transaction will go down.



When sending from an segwit address you can save about 35% of the size of the TX (and therefore from fee, since fee is usually calculated in sat/B).
It doesn't matter what address (P2PKH/P2SH) is recieving your transaction.

You should have read all the threads, articles, posts,.. which recommend how to store bitcoins securely.
Keeping 2+ BTC on an exchange (without the need of having them there) is just ridiculous.
Email is a broken protocol. I don't understand why people think its safe. Only because it is used everyday it doesn't mean it isn't completely broken.
If you didn't had 2FA activated it was just a matter of time until your account got 'hacked'.
You can depict your situation to the prosecuting authorities. But getting your money back will most likely not work out.

Before you will buy any coins again, i would recommend to read this: https://en.bitcoin.it/wiki/Storing_bitcoins

Depends on how often your hw wallet is being used. The number of write cycles onto the memory cell is the 'crucial' point.
In general they should last 7+ years if you're not using it 24/7.



A nano s isn't a backup. Its a hardware wallet which can be used for everyday payments.
The 24 word seed phrase is the backup of your private-/public keys. This phrase can be imported into any BIP39/44 compatible wallet to 'restore your coins'.

A mnemonic code is part of the Bitcoin Improvement Proposals (BIP 39: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki). Its not associated to ledger in any way.
Yes, if you do this on an 'permanently-offline' computer and noone will have access to this computer, it should be fine.
I would still recommend to move your BTC's out into a new wallet before claiming all the shitcoins altcoins.
Regard your seed as compromised from this moment on.

Actually both can store between 4 and 6 application at the same time.
The nano s has 320 kb - the ledger blue 480 kb.
The main idea behind this small storage is to limit the amound of code 'which could be injected'. Its a security 'feature'.
As far as i know the ledger team is working on an app handling all currencies. But didn't found anything regarding this on their roadmap.

The second output most likely was the change. Since you were always trying to send different amounts, different 'addresses' has been chosen to send from.
Every of your transactions had a different change which had to be confirmed on the nano s (on an older version).
You might read this: https://en.bitcoin.it/wiki/Change



They are never "stuck" in your nano s.
As long as you have stored your 24-word-seed backup, you can always recover your coins from it with any BIP39/44 compatible wallet.
Your ledger nano s is a hierarchical deterministic wallet (https://en.bitcoin.it/wiki/Deterministic_wallet).

A private key is a 256 bit number. So basically there is just 1 (very important) rule: Randomness.
The RNG is probably the most popular attack path when trying to crack (implemented) crypthographic functions.



Multiple private public keys to one address referes to hash collision:
Since there are 2^256 public keys and 2^160 addresses, there are 2^96 public keys which match to one address (on average).
 
For address collision (where 2 people accidentially generate the same address (spendable priv-/pub- keypair for this address):
Not statistics is keeping this from happening, but maths. 2^160 is about 1,460,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000.
There isn't enough energy on earth to even generate a small percentage of all of those addresses.

You don't hash the private key to get your public key. The algorithm usd is the Elliptic Curve Digital Signature Algorithm (ECDSA: https://en.bitcoin.it/wiki/Elliptic_Curve_Digital_Signature_Algorithm).
Basically its a multiplication on elliptic curves (x*y). The private key is 256 bits long and the public key is either:
1) Prefix (1 byte) + 256 bit integer (x) + 256 bit integer (y) = 520 bit (for uncompressed public keys) or
2) Prefix (1 byte) + 256 bit integer (x) = 264 bit (for compressed public keys, where the y-value can be derived from the prefix and x-value)

I hope that clears everything.

The information you gave us is very sparse.
'Server did not awnser' implies a network-kindish issue. But else.. there is nothing useful in your post. Please clarify 'addressed wallets'.
You might read the big [READ BEFORE POSTING]-thread: https://bitcointalk.org/index.php?topic=1741772.0

This does not depend on the price of sending a transaction.
The fee required to get your tx through fast depends on the amount of transactions waiting to get confirmed
and on the amount the others set as a fee. The highest bidder gets his TX confirmed the fastest.
In the early time of btc it was enough to set a fee of only a few satoshi because there weren't as much transactions done on the network as now (by far).

Your wallet seems to be fine if you can access your TX history. Your problem is the unconfirmed transaction?
Several blockchain explorer as well as my node don't find your transaction.  It does not exist on the bitcoin network.
This transaction never got confirmed back in 2014 and therefore it has been dropped from the nodes' mempool (probably also 2014).
Your address (the output of the TX) never recieved these coins.

Are you sure you have BTC's stored on your coinbase account? You may already have sold them and what you are now seeing is your FIAT balance?
If thats not the case then look at your BTC balance and/or your history. How much BTC did you buy back then and how much do you have now?
Did you eventually withdraw a small amount? Because if you aquired 0.012 BTC you should still have 0.012 on your account.
And pls keep in mind that exchanges are not recommended to store coins longer than needed for trading.

And to calculate it a bit more efficient:

current_value = old_value * (new_Price / old_Price)

current_value = 86$ * (16.000/7.000)
current_value = 86$ * (16/7)
current_value = 196,xx $

No, your change does not go to the address the transaction is made from. Core (and probably every other reputable wallet) do create a change address to recieve the change.
You can find out more about the change here: https://en.bitcoin.it/wiki/Change. Wallets tend to use addresses only once for recieving to keep a several grade of privacy.

For your own will, make sure to only work on copies from your backups. Do not change anything on your original files.

Your 'brain key' contains 'over 100 characters' and its at about 10^130, interesting.
It seems like you are using a set of 10 characters and a set of 130. Thats pretty unefficient..
Why not using a set of 62 character (a-z,A-Z,0-9) and only a length of 72 with the same entropy?

Oh.. and did you already know that bitcoin private keys are taken out of a 2^160 pool ? Thats about 10^48.
Compared to your 10^130 thats pretty weak   You can be proud to have a password which is massively stronger than the thing it protects.
Since in this scenario it is easier to crack btc and as we all know bitcoin can't be broken, such a long password may be a bit (?) paranoid, but i'll let you decide.

Thats not true. The wallet is only encrypted if you set a password to protect it. Else its not encrypted at all (encryption with an empty string doesn't count..).



Thats not true either. 'Professional programmer' can't just break cryptographical functions/methods if implemented right.
The only way for a programmer to decrypt an encrypted file (or whatever) would be if he manipulated the source code and built in a backdoor (un-)intentionally.
Usually most software runs through security audits, fuzzing, etc.. to make sure the implementation is correct and no bugs are found.
You can trust maths and cryptography but should be cautios when trusting implementations.

You should have mentioned you are talking about an online wallet earlier..
The easiest way is to call the support. Did you already do this? What did they reply? Did BitGo (your wallet provider ??) reply with the suggestion to hire a hacking service ??
This is kind of confusing.

You can't just try to bruteforce a login into an online wallet. This is (in some circumstances) part of a penetration test.
And those are not legal without permission of the website owner.