A Review on Cryptocurrency Transaction Methods for Money

Laundering

Hugo Almeida

1,2 a

, Pedro Pinto

2,3,4 b

and Ana Fern

andez Vilas

1 c

University of Vigo and AtlanTTic Research Center, Spain

Instituto Polit

ecnico de Viana do Castelo, 4900-347 Viana do Castelo, Portugal

INESC TEC, 4200-465 Porto, Portugal

Universidade da Maia, 4475-690 Maia, Portugal

Keywords:

Money Laundering, Cryptocurrencies, Blockchain, Transactions, Methods.

Abstract:

Cryptocurrencies are considered relevant assets and they are currently used as an investment or to carry

out transactions. However, speciﬁc characteristics commonly associated with the cryptocurrencies such as

irreversibility, immutability, decentralized architecture, absence of control authority, mobility, and pseudo-

anonymity make them appealing for money laundering activities. Thus, the collection and characterization

of current cryptocurrency-based methods used for money laundering are paramount to understanding the cir-

culation ﬂows of physical and digital money and preventing this illegal activity. In this paper, a collection of

cryptocurrency transaction methods is presented and distributed through the money laundering life cycle. Each

method is analyzed and classiﬁed according to the phase of money laundering it corresponds to. The result of

this article may in the future help design efﬁcient strategies to prevent illegal money laundering activities.

1 INTRODUCTION

A cryptocurrency is a virtual currency that allows

transactions, typically without the control of a cen-

tral authority (Ryan Farell, 2015). Cryptocurrencies

are based on cryptographic algorithms to secure and

legitimize transactions. They are currently highly re-

garded assets and can be used for transactions and

as an investment. The cryptocurrency transactions

take place online and, as highlighted in (Blockchain,

2021), the number of these conﬁrmed transactions in-

creased between 2010 and 2020 by more than 300,000

transactions per day. The success of cryptocurren-

cies can be related to their speciﬁc characteristics

namely their irreversibility, immutability, decentral-

ization, absence of control authority, mobility, and

pseudo-anonymity.

As cryptocurrencies can be used to make pur-

chases in any location, they have their speciﬁc value

and their transactions are not directly linked to an

identity, they can be attractive to be used in illicit

activities. According to (Foley et al., 2019) approx-

https://orcid.org/0000-0003-0803-235X

https://orcid.org/0000-0003-1856-6101

https://orcid.org/0000-0003-1047-2143

imately 46% of Bitcoin transactions and approxi-

mately 26% of all users were associated with ille-

gal activities. According to (EU, 2022), criminals

have become more sophisticated when using cryp-

tocurrencies and these currencies are used to trade

illicit goods and services, for fraud or extortion, as

part of exchanges within for-proﬁt schemes (such as

child sexual abuse material), or Money Laundering

(ML). Considering this latter and according to the

2022 Chain Analysis Report in (Crypto, 2022), there

were $8.6 Billion laundered through crypto transac-

tions, representing a 30% increase in one year and,

since 2017, there were laundered around $33 Billion

worth in cryptocurrencies.

The cryptocurrency-based ML activity compre-

hends diverse methods along the different stages of

the money laundering (ML) process. The collection

and characterization of these methods should be de-

tailed and classiﬁed, in order to understand the as-

sociated cryptocurrency ﬂows better and, as a conse-

quence, to design the most effective anti-money laun-

dering strategies.

This paper presents the methods involving cryp-

tocurrency transactions in the money laundering life

cycle. These methods are classiﬁed according to the

114

Almeida, H., Pinto, P. and Fernández Vilas, A.

A Review on Cryptocurrency Transaction Methods for Money Laundering.

DOI: 10.5220/0011993300003494

In Proceedings of the 5th International Conference on Finance, Economics, Management and IT Business (FEMIB 2023), pages 114-121

ISBN: 978-989-758-646-0; ISSN: 2184-5891

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

main stages in a ML life-cycle, i.e. placement, lay-

ering, and integration, and include the description

and analysis. The placement stage addresses the ex-

change of monetary value into cryptocurrency for fu-

ture transactions. The layering stage includes transac-

tions, splitting, and other operations with cryptocur-

rency values to avoid tracing them from their illicit

origins. The integration stage occurs when the laun-

dered value is restored back to its original owner,

without suspicion of its origin.

The remainder of this document is organized as

follows.

Section 2 describes the related work. Section 3

addresses cryptocurrency transactions. Section 4

presents the cryptocurrency-based ML. Section 5 de-

tails and discusses the proposed method distribution

through each money laundering phase. Section 6

presents the conclusions.

2 RELATED WORK

As a digital currency, cryptocurrencies are part of a

digital monetary system that allows transactions of

any amount of value in that format. The control of

a given cryptocurrency can be centralized or decen-

tralized. In case the control of the cryptocurrency is

decentralized, it may use Blockchain as the founda-

tional technology. Blockchain can be deployed us-

ing a public registry, distributed on an extensive net-

work of computers that veriﬁes in real time all trans-

actions involving cryptocurrencies (Nakamoto, 2008;

Hayes, 2022; Albrecht et al., 2019). Each transac-

tion is recorded anonymously, and depending on the

cryptocurrency proﬁle used, it can be more or less dif-

ﬁcult to trace. Each block is timestamped when it

is included in the blockchain which is structured in

chronological order.

Since transaction codes are recorded on the

blockchain using a cryptographic algorithm, changing

the elements of a previous transaction is not feasible.

Cryptocurrencies using blockchain inherit the

property of pseudo-anonymization, allowing one to

check the address of the wallet, but not the user iden-

tity (Yuan and Wang, 2018; Dupuis and Gleason,

2020). This property along with being decentralized

without central control, but secure at the same time,

enables blockchain cryptocurrencies to be used for il-

licit actions, such as Money laundering.

As stated in (Suratkar et al., 2020), cryptocur-

rency wallets are used by any person or entity wish-

ing to transact cryptocurrencies. They are useful to

store data related to the cryptocurrency transactions of

their holder. Unlike a normal wallet, cryptocurrency

wallets do not store physical currency, they store the

keys that allow you to access your cryptocurrencies

and perform the transactions you intend with them.

There are different types of cryptocurrency wallets:

- Desktop wallets: Software that can be installed on

a computer; - Online wallets: Software that works

via the internet, hosted in such a way that it can

be accessed from anywhere; - Mobile wallets: Soft-

ware that works on mobile devices; Hardware wallets:

Physical wallets that can be carried and stored outside

the digital world, they usually have a look similar to a

pen drive;

According to (Han et al., 2020) Money Launder-

ing can be deﬁned as ”transferring illegally obtained

money through legitimate persons, accounts, or ser-

vices so that its original source cannot be discovered”.

Money laundering constitutes a set of behavioral pat-

terns. In (Faccia et al., 2020) it is implied that money

in this process, is associated with a group of behav-

ioral patterns, namely, replacement behavior (where

any relationship with the source of the money is elim-

inated), transfer behavior (through the use of illicit

value transaction instruments for different purposes),

and the undertaking of other operations aimed at recy-

cling this money, outside the scope of the legislation

in place. Money laundering through cryptocurren-

cies refers to the process of converting, through trans-

actions of cryptocurrencies and other assets, illicitly

obtained ﬁnancial resources, into legitimate currency

and integrating them into the ﬁnancial system.

In (Teichmann and Falker, 2020) authors explore

how cryptocurrencies can be used in money launder-

ing. The authors claim that unregulated cryptocur-

rencies pose a threat to lawmakers and law enforce-

ment. These cryptocurrencies are considered high

risk due to the pseudo-anonymity characteristic, and

despite the fact that their usage requires some techno-

logical knowledge, there are ample resources to over-

come this problem. The authors argue that to avoid

money laundering with cryptocurrencies, institutions

and people dealing with this asset should avoid con-

ducting transactions if they have any doubts.

According to Chainanalisys (Team, 2022)

cryptocurrency-related crimes broke records in 2021.

The amounts moved to illicit wallets reached 14

billion that year, up from 7.8 billion the previous

year. These measures are important for restricting

access and creating mechanisms to enable further

and more thorough investigation of cryptocurrency

transactions and proﬁts. In (Foley et al., 2019) the

authors quantify and characterize the illegal bitcoin

trade; and also state that cryptocurrencies are among

the largest unregulated markets in the world. It is

found that approximately one-quarter of bitcoin users

A Review on Cryptocurrency Transaction Methods for Money Laundering

115

are involved in illegal activity and that bitcoin is

related to around 76 billion of illegal activity per year,

which is near the volume of the U.S. and European

markets for illegal drugs. Their ﬁndings suggest that

cryptocurrencies are transforming the black markets

by enabling “black e-commerce.”

Authors in (Dyntu and Dykyi, 2019) analyze com-

pliance risks associated with cryptocurrencies, partic-

ularly investigating how cryptocurrencies can be mis-

appropriated to launder money. It demonstrates how

criminals use cryptocurrencies to circumvent existing

Anti Money Laundering (AML) measures. As regular

cryptocurrencies like Bitcoin are not regulated, they

pose immense compliance threats from the perspec-

tives of legislators and law enforcement. The authors

highlight that, to be able to effectively prevent money

laundering, authorities must understand how money

launderers act. Their study provides valuable insight

into criminals’ perspectives, it partially ﬁlls the iden-

tiﬁed literature gap by illustrating how money laun-

derers operate using cryptocurrencies.

In the ﬁnancial system, a group of authors such

as (Schneider and Niederl

ander, 2008; Reuter and

Truman, 2004; Brenig et al., 2015) identify a set of

phases for the money laundering process. According

to (Liu et al., 2021; Wronka, 2021a; Wronka, 2021b),

a classical model featuring the following three phases

is highlighted: Placement, Layering, and Integration.

The Placement phase aims to eliminate all links be-

tween the illegal value and its origin or ownership.

The Layering phase is the process of transferring

funds through different applications or accounts so

that the initial origin of the money is difﬁcult to ﬁnd.

The Integration phase is where the funds are inte-

grated into the legitimate economy.

3 TRANSACTIONS AND

WALLETS

To perform cryptocurrency transactions it is neces-

sary to use cryptocurrency wallets, depending on their

type. Cryptocurrency wallets can be categorized with

respect to their operation, by the following types:

• Hot - wallets that need an internet connection to

operate;

• Cold - wallets that consist of hardware devices

that do not need internet access to maintain the

data

In addition to this dependency, cryptocurrency wallets

can also be categorized with respect to their manage-

ment, i.e.:

• Custodial - wallets managed by a third entity, i.e.

their private keys are the property of that entity,

which happens in the case of wallets integrated

into exchanges

• Non-custodial - wallets where the owner has full

control of the funds and the private key associated

with the wallet.

Crypto wallets can interact with multiple types of

cryptocurrencies and some of these wallets are more

geared toward maintaining anonymity. The Cold and

non-custodial wallets are the ones offering low expo-

sure, however, a higher degree of liability is required,

because if the private key is lost, it will not be re-

coverable. Also, they can have features such as non-

reuse of addresses associated with transactions; use of

route access via TOR and using VPN; use of the Coin-

join protocol; creation of hidden wallets in the appli-

cation interface; automated behavior settings that al-

low automatic sending of funds under certain condi-

tions such as described in (Taylor et al., 2022; Thomp-

son, 2022; Clarke, 2022). However, the characteris-

tics and usefulness with regard to privacy and pseudo-

anonymity of cryptocurrency wallets are constantly

changing. With the increasing government controls

and Know Your Customer (KYC) measures, the type

of the wallets may change or be blocked (Hay, Steven,

2022).

4 CRYPTOCURRENCY-BASED

In the current study, a set of cryptocurrency transac-

tion methods is reviewed in the context of the money

laundering life cycle. The choice of these methods

was centered on ease of access, computer knowledge

only necessary from the user’s point of view, basic

knowledge in the world of cryptocurrencies, the pos-

sibility of using any computer with only an internet

connection, and the possibility of maintaining a min-

imum level of privacy.

The cryptocurrency methods collected are In-

Person Transaction, Crypto ATM Machines, P2P

Transactions, Prepaid or Gift Cards, Tumblers or

Mixing Services, Chain Hopping, Decentralized Ex-

changes, Cryptocurrencies Online Casinos, and In-

vestments Through Cryptocurrencies. These are de-

scribed in the following sections and mapped in the

three classical phases of the money laundering life cy-

cle, i.e. Placement, Layering, and Integration.

FEMIB 2023 - 5th International Conference on Finance, Economics, Management and IT Business

116

4.1 In-Person Transaction

The In-Person Transaction can be a purchase (in the

Placement phase) or a sale (in the Integration phase).

For purchase, this method requires, ﬁrst, ﬁnding

someone that has a given amount of cryptocurrency.

Next, each person should agree on the price of the

coins and make the exchange manually. This implies

a certain degree of trust between the parties involved,

on the other hand, the storage device of the cryptocur-

rencies or the platform where they are to be trans-

ferred must be carefully analyzed and thought through

beforehand.

For the sale, and from the seller’s perspective, this

method implies a degree of trust between the parties

involved. In case the transaction is accomplished and

anonymity is maintained, however, the volume trans-

acted and the insertion of ﬁat currency in the ﬁnancial

system can generate alerts for further investigation re-

garding the origin of these values, raising legal and/or

ﬁscal issues. Another important issue is the cryp-

tocurrency value set for the transaction. A downside

is that the value is not stable, therefore, is important

to check whether it meets the established criteria so

that the deal is carried out proﬁtably (Cointelegraph,

2021).

4.2 Cryptocurrency ATM Machines

The Cryptocurrency ATM Machines method can be a

deposit (in the Placement phase) or a withdrawal (in

the Integration phase).

For the deposit, the cryptocurrency ATMs are ter-

minals connected to the internet that allows users to

buy cryptocurrencies. These machines connect to the

bitcoin network and allow users to buy and sell cryp-

tocurrencies. They are generally not related to known

ﬁnancial entities (e.g. banks). As an advantage, there

is the possibility to perform transactions using any

normal cash ATM. Also, anonymity is still allowed

in this method. Despite the increasing implementa-

tion of KYC measures, there are several operators,

with different models of machines with diverse char-

acteristics and identiﬁcation requirements, from min-

imal (e.g. Qr code) to demanding systems (e.g. facial

recognition). However, the following aspects should

be taken into account: Cryptocurrency ATMs are not

abundant; their offer in terms of transactions is lim-

ited in number and choice of cryptocurrencies; their

fees are varied (statistics in (News et al., 2021) show

that the average worldwide fees are 8.4% to buy bit-

coins in Cryptocurrency ATM machines, and 5.4% to

sell and exchange for real money).

Regarding withdrawal, the cryptocurrency ATM

machines allow interaction with both types of cur-

rencies, cryptocurrencies and regular. They have a

similar interaction to any other normal ATM machine

and they are accessible in urban environments thus,

cryptocurrency ATM machines can be used to con-

vert cryptocurrencies into physical currency, such as

euros or dollars. As mentioned in (Jurva, Gina, 2022),

it is relatively easy to withdraw money from a cryp-

tocurrency ATM without having strict control. For

instance, if it is needed to withdraw $15000 (USD),

the person needs to use several different cryptocur-

rency ATMs and withdraw the stipulated maximum

limit until the required amount is reached.

4.3 Peer to Peer (P2P) Transactions

The P2P Transaction method can consist of a pur-

chase (in the Placement phase) or a sale (in the In-

tegration phase).

In the purchase, P2P, represents a transaction be-

tween two peers through a communication channel

without the control or monitoring of a regulatory en-

tity. This transaction can be performed by dedicated

platforms, executing the following steps: ﬁrst, it is

necessary to ﬁnd the partner to make the transaction,

then it is necessary to deﬁne the format for sending the

monetary value in ﬁat currency, and ﬁnally, schedule

and carry out the transaction.

The already available platforms allow you to se-

lect a speciﬁc seller for a given transaction. The fol-

lowing preventive measures should be taken into ac-

count: analyze the reputation of the transaction part-

ner; understand the way the platform works, check

the reputation of the platform itself, and ﬁnally pre-

pare the way the cryptocurrency is received. How-

ever, this method has some limitations, the value of

the currency is usually higher than the market value

and the quantity is limited.

Regarding the sale in the integration phase, this

means it can be also used to sell or convert the cryp-

tocurrency into real currency. The level of reputation

of a user can be an inﬂuential factor even in ﬁnding

someone receptive to transact. In some platforms, de-

pending on the choice, it is still possible to proceed

without KYC rules, however, the transaction partner

may ask for identity veriﬁcation in case of a bank

transfer.

4.4 Prepaid or Gift Cards

This method is performed when there are means of

housing pre-stipulated amounts of money on a plas-

tic card that allows purchases to be made through a

code. There are two differences between prepaid and

A Review on Cryptocurrency Transaction Methods for Money Laundering

117

gift cards: the ﬁrst is that prepaid cards can generally

be loaded indeﬁnitely, while gift cards can only be

used until the amount they contain is used; the second

difference is that prepaid cards are generally associ-

ated with a ﬁnancial interest entity, banks, or credit

companies, while gift cards are generally associated

with a speciﬁc retailer, for instance, clothing shops,

app shops, online games, etc.

Prepaid credit cards are under surveillance by gov-

ernment entities and under anti-money laundering di-

rectives imposed by the European Union (EU) on

member states, attempting to limit the activities of ID-

less prepaid cards.

Alternatively, in the placement phase, the trans-

action can be performed through gift cards from the

most popular platforms, from online shopping to mo-

bile phone operating system app shops. However,

transaction costs are high and the volumes involved

are limited; for the current study, it was tried out the

platform PaxFul (Paxful, Inc., 2021), which allows

Bitcoin (BTC) purchases of up to 4000 euros on pre-

paid cards from a gaming platform, available in any

supermarket or technology shop.

Also, a card sale is also a possibility in the inte-

gration phase. This is a method used also in the inte-

gration phase, as it is possible to buy gift cards with

cryptocurrencies, where these values are already ear-

marked for one or several speciﬁc purchases of goods

available on large online trading platforms such as

Amazon, Apple, eBay, etc. Currently, these platforms

do not accept purchases with cryptocurrencies, but it

is possible to buy gift cards for later use without the

need for personal data, since they are not issued to the

bearer, thus guaranteeing anonymity. The purchase

assets are limited to the card and its lifetime may be

limited also, however, its representative value remains

regardless of exchange rates. There are several plat-

forms for the purchase of gift cards with cryptocur-

rencies that have minimum requirements for registra-

tion, although some have speciﬁc characteristics, the

variety of products and retailers is vast, which allows

you, at the limit, in some countries, to live anony-

mously using cryptocurrencies via gift cards. (Rees,

Katie, 2022; BitShills, 2022)

4.5 Tumblers or Mixing Services

Tumblers or Mixers are services that, through soft-

ware, aim to reduce the identiﬁcation of the prove-

nance of cryptocurrencies by mixing several trans-

actions together. Since transaction data is public,

with speciﬁc procedures, it is possible to identify

data relating to a particular transaction, such as its

origin, value, and other readable data. The goal of

this method is then to divide the funds to be trans-

acted into smaller sets, which can then be mixed with

other transactions. When the process is over, the re-

ceiver receives the same value but in a new set of

coins. Thus, a tumbler allows breaking the relation-

ship that exists between your ID and the cryptocur-

rency owned, and it can be used in the Layering phase

of the money laundering life cycle.

4.6 Chain Hopping

Chain Hopping is another Layering method, which

can be referred to as a generally fast succession of

transactions between different blockchains and cryp-

tocurrencies, to make it harder to trace the origin

and the destination of the exchanged monetary val-

ues. These transactions are done through different ex-

changes less demanding in terms of regulation (Kelly,

Jemima, 2017; Wilkinson, Monty, 2021), and so they

are used in the Layering phase of the money launder-

ing life cycle.

4.7 Decentralized Exchanges

A decentralized exchange is a peer-to-peer exchange

where cryptocurrency transactions can take place be-

tween two entities, buyers and sellers. This type of

exchange does not have an entity regulating the trans-

action, i.e., it does not have intermediaries with all the

beneﬁts and risks that this entails. To this date, these

types of exchanges only transact between cryptocur-

rencies, they do not use ﬁat money. Also, they do not

need detailed personal information and there are no

unnecessary transfers of assets, which allegedly de-

creases the risk of theft. Finally, they also have a large

variety of different crypto assets although their liquid-

ity, volume, and supply are not exactly the same as in

centralized exchanges. This is a method used in the

Layering phase of the money laundering life cycle.

4.8 Cryptocurrency Online Casinos

Casinos have always been a possibility for money

laundering. When using cryptocurrencies, crypto on-

line casinos can be a possible method in the con-

text of the Layering phase of the money launder-

ing life cycle. According to (Markoski, 2021), the

cryptocurrency-based gambling market has shown

stable growth in the last few years with an aggregate

value of more than $150 million. These platforms can

be an option if the criminal seeks anonymity and want

to avoid the control of tax authorities.

The advantage of these transactions is that they

depend on the casino’s KYC measures that, when re-

FEMIB 2023 - 5th International Conference on Finance, Economics, Management and IT Business

118

Table 1: Cryptocurrencies-based Money Laundering Methods.

Methods Placement Layering Integration

In-Person Transactions • – •

Crypto ATM Machines • – •

P2P Transactions • – •

Prepaid or Gift Cards • – •

Tumblers or Mixing Services – • –

Chain Hopping – • –

Decentralized Exchanges – • –

Cryptocurrencies Online Casinos – • –

Investments Through Cryptocurrencies – – •

laxed, help maintain the anonymity of the transactions

made anywhere in the world.

4.9 Investments Through Crypto

There are multiple ways to convert cryptocurrency

into physical cash, e.g. to buy property or goods with

cryptocurrencies and then sell these items for physi-

cal cash. According to (Heaven, Douglas, 2018), in

September 2017, a ﬂat in Kyiv worth $60,000 be-

came the ﬁrst property to be sold using blockchain.

The transaction took place entirely on the Ethereum

blockchain, through smart contracts and using cryp-

tocurrencies. Also in September 2017, on the 18th,

according to (Realty, Kuper Sotheby’s International,

2018), a house was sold through a cryptocurrency

transaction for the ﬁrst time in that state. (Idealista.pt,

2022) states that the ﬁrst house in Portugal involved in

a cryptocurrency transaction was sold on 5 May 2022

for 3 BTC, which, at the time, was worth 110,000 eu-

ros. In this type of transaction, the value of the good

is only factual at the time of the transaction given the

rate of change of virtual currencies. At the time of this

writing, 3 BTC is worth 57,978.91 euros, but those

who bought the house, still have a property with its

value intact on the market, like all others. Thus, this

is a method that can be used in the Placement phase

of the money laundering life cycle.

5 DISCUSSION

Table 1 presents the mapping between the analyzed

cryptocurrency transaction methods and the phases of

money laundering where they are used: Placement,

Layering, and Integration. In-Person Transactions,

Crypto ATM Machines, P2P transactions, and Prepaid

or Gift Cards can be used in Placement and Integra-

tion phases. Tumblers or Mixing Services, Decen-

tralized Exchanges, Chain Hopping and Cryptocur-

rencies Online Casinos can be used Layering phase.

Investments Through Cryptocurrencies can be used

in the Integration phase. The selection of the meth-

ods was performed from the standpoint of someone

intending to launder money with cryptocurrencies,

without having speciﬁc technical knowledge. In the

case of a presence of a technical expert, the list of

methods presented would be more extensive. The an-

alyzed methods may have a short life span since the

illicit nature of these procedures makes their sources

or sites deactivated, removed, or fall into disuse.

6 CONCLUSIONS

As cryptocurrencies can be used to buy assets in any

location and their transactions are not directly linked

to an identity, they can be attractive to be used in illicit

activities among them, money laundering.

This paper reviews a set of cryptocurrency Trans-

action Methods used in the context of Money Laun-

dering activities. Each method included is detailed

and contextualized in the phases of the Money Laun-

dering life cycle. The review produced the mapping

and categorization of some of the most commonly

used methods in the different stages of cryptocurrency

money laundering. As a result, this work may in the

future aid the design of efﬁcient strategies to prevent

illegal money laundering activities.

As future work, these methods can be tested and

evaluated in multiple strands such as complexity, time

spent, stakeholders, purpose, technological require-

ments, environment, difﬁculty, etc. Also, there is

a need to survey the current anti-money laundering

measures and regulations for the cryptocurrency mar-

kets, to check their efﬁcacy to counter the money

laundering methods. Money laundering techniques

are constantly evolving and, as a consequence, anti-

money laundering efforts should be developed as a

countermeasure to these illegal activities.

A Review on Cryptocurrency Transaction Methods for Money Laundering

119

ACKNOWLEDGEMENTS

This work has received ﬁnancial support from the Eu-

ropean Regional Development Fund (ERDF) and the

Galician Regional Government, under the agreement

for funding the Atlantic Research Center for Informa-

tion and Communication Technologies (atlanTTic).

This work was also supported by the Spanish Gov-

ernment under re-search project “Enhancing Commu-

nication Protocols with Machine Learning while Pro-

tecting Sensitive Data (COMPROMISE)” (PID2020-

113795RB-C33/AEI/10.13039/501100011033).

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